Journal of Animal and Feed Sciences, 16, Suppl. 1, 2007, 7–20


Prospects of obtaining favourable fatty acid composition of cows milk by feeding


K. Sejrsen1, T. Bjørn and S.K. Jensen


University of Aarhus, Faculty of Agricultural Sciences, Research Centre Foulum

P.O. Box 50, DK-8830, Tjele, Denmark


ABSTRACT


Information from the literature and own data show that the ratio of unsaturated to saturated fatty acids in milk fat, the level of CLA and ω-3 fatty acids can be improved by dietary factors. However, none of the components can be changed without a concomitant increase in trans fatty acids, some with unknown human health effects. Diets that effectively affect milk fat composition, often lead to milk fat depression due to inhibition of expression of the genes coding for key enzymes. Potential negative effects on technological and sensory quality cannot be ignored.


KEY WORDS: unsaturated fat, CLA, trans fatty acids, milk fat depression, gene expression, antioxidants, vitamin E


INTRODUCTION


Despite a decrease in the relative value of milk fat compared to milk protein, the demand for milk fat is likely to remain high. This is mainly due to its essential impact on the organoleptic quality of milk and most milk products, but also for cultural reasons. However, the image of milk fat has been tainted by the negative human health effects attributed to dietary fat in general and milk fat especially. The alleged negative human health effects include increased risk of cardiovascular diseases and cancer (Williams, 2000; Moorman and Terry, 2004; Mozaffarian et al., 2006).

The negative effects of milk fat have been linked to its high content of saturated fat (up to 65%), especially the short and medium chain fatty acids. Negative health effects of dietary fat have also been linked to low content of ω-3 fatty acid, especially when the ratio of ω-3 to ω-6 fatty acids is low. In milk fat the content of ω-3 is low,


image

1 Corresponding author: e-mail: kr.sejrsen@agrsci.dk


but the ratio of ω-3 to ω-6 can be rather high. More recently negative health effects of dietary fat have also been linked to mono-unsaturated fatty acids, especially trans- fatty acids from industrial saturation of vegetable fat. Milk also contains trans-fatty acids, but no negative effects have been linked to the main trans-fatty acid isomer in milk fat, trans-11 C18:1 (also called vaccenic acid). Nevertheless, milk can contain considerable amount other trans-fatty acid, such as trans-10 C18:1. In contrast to these negative effects linked to the composition of milk fat, potential positive health effects has been linked to conjugated linoleic acids (CLA) present only in fat from ruminants, especially milk fat (Bauman et al., 2006).

As a consequence of the general negative view of the health effects of milk fat, the potential for changing milk fat composition has been widely investigated. The prospects for altering milk fat composition through dietary changes are good, because fatty acids from feed are incorporated directly into milk, and can constitute up to 60% of the fatty acids in milk. In recent years much research has focused on the potential for increasing the amount of CLA.

In line with the large body of work carried out, a large number of reviews are available on the topic. Yves Chilliard from INRA is the author of several excellent reviews on the effect of nutrition on milk fat composition; among these are Chilliard et al. (2000, 2001) and Chilliard and Ferlay (2004). Dale Bauman and co-workers have written reviews on milk fat composition with special attention to CLA, such as Griinari and Bauman (1999), Bauman and Griinari (2003) and Bauman et al. (2006). We would also like to draw the attention to recent reviews by Jensen (2002), Dewhurst et al. (2006) and Jenkins and McGuire (2006).

It is the objective of this paper to give a brief overview of the topic illustrated mainly by examples from own data. We refer to the reviews mentioned for a more detailed coverage of the topic.


MILK FAT SYNTHESIS


As mentioned above, milk fat consists of up to 60% preformed fatty acids taken up directly from the feed. The rest is synthesized de novo in the mammary gland from acetate and beta-hydroxy butyrate originating from microbial fermentation of polysaccharides in the rumen. The key regulatory enzymes of de novo milk fat synthesis are acetate CoA carboxylase (ACC) and fatty acid synthase (FAS). The activities of these enzymes are inhibited by long chain fatty acids, especially unsaturated long chain fatty acids.

The fatty acids synthesized de novo are all saturated and the chain length is variable but not higher than 16. The short chain (C4:0-C8:0) and medium chain (C10:0-C14:0) fatty acids originate almost exclusively from de novo synthesis. Approximately 50% of C16:0 originate from de novo synthesis. The activity of


the desaturase enzyme in the mammary gland is low for fatty acids with chain length below 16. Therefore almost all fatty acids synthesized de novo are remain saturated.

The long chain fatty acids in milk originate almost exclusively from the feed except in early lactation, where fatty acids mobilized from body stores contribute to a minor degree. Consequently, the composition of the long chain fatty acids in milk fat reflects the fatty acid composition of the feed but only to some extent because the ingested fatty acids undergo considerable modifications in the animal body. The modifications occur partly in the rumen and partly in the mammary gland. In the rumen the fatty acids undergo isomerization and hydrogenation. The rumen modifications depend to a large extent on the fatty acid composition of the fat in the ration, but other factors, such as starch and fibre content, that affect rumen fermentation also play a role. The modifications in the mammary gland are catalysed by desaturation enzymes, especially delta-9-desaturase that converts trans-11 C18:1 to cis-9, trans-11 C18:2, the most abundant CLA and C18:0 to C18:1.

The majority of the fatty acids in milk (97-98%) are incorporated into triglycerides before being excreted into the milk in lipid droplets coated by the milk fat globule membrane (Jensen, 2002).


DIETARY MANIPULATION OF MILK FAT COMPONENTS


Dietary factors


The potential for altering milk fat composition by dietary means is good - within limits. Overall, the milk fat composition can be altered both by the amount and the fatty acid composition of the diet as well as choice of forage type and forage: concentrate ratio.

The fatty acid content varies widely between feedstuffs. It ranges from 1-3% in most forages, including pasture, up to 95% in vegetable oils. The composition of the fatty acids also varies considerably among feedstuffs. In maize silage almost 50% of the fat is linoleic acid and only around 5-10% is linolenic acid. In contrast, grass silage contains 50% linolenic acid and less than 10% linoleic acid. Sunflower oil contains more than 60% linoleic acid and almost no linolenic acid, whereas linseed oil contains approximately 50% linolenic acid and only 15% linoleic acid. The ratio of linoleic to linolenic acid is important due to the different dehydrogenation pathways in the rumen (Griinari and Bauman, 1999). Fresh grass and fish oil are good sources of ω-3 fatty acids.

In view of these large differences in fatty acids content and fatty acid composition

it is possible to create rations with very different amount and composition of fatty acids. Due to the importance of the rumen modifications, factors influencing the


rumen environment, such as forage: concentrate ratio and starch content, also affect milk fat composition.


Saturated and unsaturated fatty acids


The obvious way to alter the ratio between saturated and unsaturated fatty acids in milk is to increase the amount of unsaturated fat in the diet. This leads to an increase in the amount of unsaturated long chain fatty acids in milk fat, even if a considerable part of the unsaturated fatty acids are hydrogenated in the rumen. This is illustrated by results from one of our experiments (Nielsen et al., 2005a), where cows were fed increasing amount of sunflower seeds (Experiment 1). Intake and milk production data are shown in Tables 1 and 2.


image

image

image

Table 1. Influence of diet composition on intake of DM, fatty acids and starch Treatment Intake per day

lipid source

forage DM FA C18:2 C18:3 starch

type kg g g g g

Experiment 1

sunflower1

0

17.9

376

149

85

3565

5

grass

17.5

771

397

83

3312

10

silage

14.4

963

534

69

2371

15% of DM

14.6

1318

760

72

1405

P

*

*

*

*

*

Experiment 2

fat source (S)2

rape seed maize

+ vit. E silage

sunflower

20.1

1244

261

100

4808

17.8

1101

231

89

4254

19.7

1103

546

12

4590

+ vit E

PA- S/E/X

20.4

NS/NS/*

1144

NS/NS/*

566

*/NS/NS

12

*/NS/NS

4753

NS/NS/*

Experiment 3

forage type (F)3


grass silage


18.4


957


211


180


70

+ barley (B)

19.4

985

275

167

1948

rapeseed

cakes

maize silage

18.4

1139

345

105

3818


PA- F/B/X

+ barley (B)

20.0

NS/*/NS

1260

*/*/NS

390

*/*/NS

114

*/NS/*

4874

*/*/*

1 Nielsen et al., 2006a; Sejrsen and Bjørn, unpublished; n=24; 2 Sejrsen and Schaltz, unpublished, n=40; 3 Nielsen et al. (2006), n=40; * - P<0.05; A effect of main factors: S - fat source; E - vitamin E supplementation; F - forage type; B - barley supplementation; X - interaction, * P<0.05; NS - no

significant difference


image

image

image

Table 2. Influence of diet composition on feed intake, milk yield and milk fat content Treatment Yield per day

lipid source

forage milk fat fat

type kg % g

Experiment1

sunflower1

0

28.9

3.8

1095

5

grass

26.5

3.8

971

10

silage

22.0

4.0

924

15% of DM

21.0

4.4

884

P

*

NS

NS

Experiment 2

fat source (S)2

rape seed maize 32.0

3.17

1013

+ vit. E silage 27.5

3.01

815

sunflower 28.5

3.97

1160

+ vit E.

28.5

4.03

1116

PA- S/E/X

NS/*/*

*/NS/NS

*/*/NS


Experiment 3

forage type (F)3

grass silage

24.4

4.16

1003

rapeseed

+ barley (B)

25.6

4.13

1053

cakes

maize silage

23.4

3.41

786

+ barley (B)

23.7

3.05

726

P- F/B/X NS/NS/NS */NS/NS */NS/NS

1 Nielsen et al., 2006a; Sejrsen and Bjørn, unpublished. n=24; 2Sejrsen and Schaltz, unpublished, n=40; 3 Nielsen et al. (2006), n=40; * - P<0.05; A effect of main factors: S - fat source; E - vitamin E supplementation; F - forage type; B - barley supplementation; X - interaction, * P<0.05; NS - no significant difference


As the inclusion of sunflower oil increased so did the ratio between long (chain length >16) and short chain fatty acids (chain length <16) (Table 3) as well as the relative part of unsaturated fatty acids in the long chain fatty acids.

The type of unsaturated fatty acids can also be altered by the type of lipid supplement used (Chilliard et al., 2000; Chilliard and Ferlay, 2004). We intended to study this effect in another experiment (Experiment 2) where we compared the effect of rape seed and sunflower cakes - not seeds as in the previous experiment (Sejrsen and Schaltz, unpublished). The intention was to study the effect of changing the ratio between linoleic and linolenic acid in the diet. As can be seen in Table 1, the intakes of fatty acids were similar on both treatments. This can be confirmed by the effect of vitamin E-status (Table 5). As expected the relative amount of long chain fatty acids in milk from the cows fed rape seed was very high - 60% - and the


relative amount of unsaturated fatty acids in the long chain fatty acids was also high

- compared to the milk fat from the control cows in the experiments with sunflower seeds (Experiment 1) (Table 3). The unexpected lack of increase in long chain and unsaturated fat in the milk from cows receiving the sunflower cakes, indicate that the lipids from these cakes were not absorbed from the small intestine probably due to events during handling of the seeds during processing.


image

image

image


lipid source


forage

type


4

% of total FA


5

% of total FA


C18:1-3

% of LCFA

Experiment 1

sunflower 1

0

33.8

35.1

47.6

5

grass

27.4

46.3

50.6

10

silage

22.8

56.2

56.4

15%

21.2

58.5

58.1

P

*

*

*


Experiment 2

fat source (S)2

rape seed

+ vit. E sunflower


maize silage

21.2

20.2

32.5

60.1

60.8

38.3

56

58

42

+ vit E.

33.0

38.3

43

PA - S/E/X

*/NS/NS

*/NS/NS

*/NS/NS


Experiment 3

forage type (F)3

grass silage

21.0

55.1

50

rapeseed

+ barley

21.5

54.9

51

cakes

maize silage

18.2

60.6

58

+ barley

17.6

61.3

58

calculated from mean values

Table 3. Influence of diet composition on short chain, long chain and unsaturated fatty acids in milk fat1 Treatment Fatty acid composition

<C16 - SCFA

>C16 - LCFA


1 Nielsen et al., 2006a; Sejrsen and Bjørn, unpublished, n=24; 2 Sejrsen and Schaltz, unpublished, n=40; 3 Nielsen et al. (2006), n=40; 4 SCFA - short and medium; 5 LCFA - long chain fatty acids; chain fatty acids; * - P<0.05; A effect of main factors: S - fat source; E - vitamin E supplementation; F

- forage type; B - barley supplementation; X - interaction, * P<0.05; NS - no significant difference


This underlines the importance of the availability of the lipids from the feeds. Due to the hydrogenation in the rumen, the transfer of unsaturated fatty acids feed to milk is relatively low and it decreases with increasing level in the feed. To increase the transfer encapsulation of the oil can be used to prevent the lipid


hydrogenation in the rumen. This can be an effective tool (Chilliard et al., 2000). The transfer efficiency also varies between different feedstuffs and depending on the treatment of the lipid supplement (as unfortunately illustrated in our experiment).

In a third experiment (Tables 1 and 2) we have confirmed the importance of the basal diet for milk fat composition (Nielsen et al., 2006). In contrast to most other comparisons of forage types we compared grass silage with maize silage using diets with high level of supplementation of unsaturated fat - in this case rape seed. In most comparisons of grass silages with maize silage without extra lipid supplementation the highest content of unsaturated fatty acids in milk is found when the grass or clover based diets are fed. Our results, in contrast, show the highest level of preformed fatty acids and the highest content of unsaturated fatty acids in the milk fat from the cows on the maize silage diet (Table 3). The reason most likely is due to an effect on rumen fermentation caused by the high starch content. We found a significant positive relationship between starch intake and milk content of several unsaturated fatty acids. This hypothesis is supported by the exacerbation of the effect by increasing the level of barley in the diet. The interaction between forage type and lipid content is thoroughly treated in the review by Chilliard and Ferlay (2004).

In summary, the ratio of saturated to unsaturated fat can be altered considerably by the amount and source of fat in the diet. The ratio is also affected by the type of forage used in the basal diet. In our experiments we were able to increase the level of preformed fatty from 35 to over 60% of the milk fat and the content of unsaturated fatty acids in the long chain fatty acids could also be increased considerably, from 40 to almost 60%. The change in the content of unsaturated fatty acids is caused partly by the transfer of unsaturated fat into milk and partly by a negative effect of unsaturated fatty acids on de novo milk fat synthesis (see later).


Trans-fatty acids


Increasing the amount of unsaturated fatty acids in the diet increases the amount of trans fatty acids in milk fat. The results of our experiments are in agreement with this conclusion (Table 4). From our results it is obvious that the increase in total trans fatty acids is highest when the unsaturated fatty acids are fed in combination with maize silage and that the effect is exacerbated by adding extra barley/starch to the diet. A further effect is that the higher level of trans fatty acids involves a shift from trans-11 to trans-10 C18:1. In our experiment comparing grass silage with maize silage, the ratio of trans-10, to trans-11 in milk fat increased from 0.3 to 1 on the grass silage diet to 3.9 to 1 on the maize silage diet at the highest level of barley inclusion. The highest average concentration of trans-10 (6.05% of milk fatty acids) in milk was observed on the diet consisting


of rapeseed cakes given with maize silage and high level of barley. The relevance of this for human health is not certain (see later).


image

image

image

Table 4. Influence of level of diet composition on trans fatty acids and CLA in milk fat1 Treatment Fatty acid composition, % of total FA

lipid source

forage trans FA trans-11 trans-10 cis-9, trans-11

type total C18:1 C18:1 CLA

Experiment 1

1.04

1.04

-

0.46

2.55

1.98

-

0.69

3.87

3.06

-

1.07

4.05

3.21

-

1.33

*

*

*


8.64


2.48


4.05


1.20

9.25

1.80

5.11

1.28

1.87

0.55

0.41

0.29

1.93

0.54

0.51

0.30

*/NS/NS

*/NS/NS

*/NS/NS

*/NS/NS


4.86


1.74


0.60


0.89

5.08

1.79

0.66

0.92

9.25

2.80

3.14

1.61

10.53

1.55

6.05

1.17

*/NS/NS

NS/*/*

*/*/*

*/*/*

sunflower 1

0

5

10

15% of DM P


Experiment 2

fat source (S)3 rape seed

+ vit. E sunflower

+ vit E. PA - S/E/X


Experiment 3

forage type (F)2


rapeseed cakes


P- F/B/X

grass silage


maize silage


grass silage

+ barley (B) maize silage

+ barley

  1. Nielsen et al., 2006a; Sejrsen and Bjørn, unpublished, n=24; 2 Sejrsen and Schaltz, unpublished, n=40; 3 Nielsen et al. (2006), n=40; * - P<0.05; A effect of main factors: S - fat source; E = vitamin E supplementation; F - forage type; B - barley supplementation; X - interaction, * P<0.05; NS - no significant difference


    So in summary, the same diets that result in improved ratio between saturated and unsaturated fatty acids cause an increase in trans fatty acids, especially when given in combination with diets containing high levels of starch. These diets also cause a switch in the ratio of trans-11 to trans-10 C18:1.


    CLA


    CLA (cis-9, trans-11 conjugated linoleic acid) is formed in the rumen via

    biohydrogenation of linoleic acid and in the mammary gland by desaturation of


    trans-11 C18:1 formed via the biohydrogenation of both linoleic and linolenic acid in the rumen. Therefore the level of CLA in milk can be raised by addition of unsaturated fatty acids to the diet. We observed the same in our experiment with increasing level of sunflower (Table 4). Usually the CLA is higher in milk from cows fed grass based diets compared with maize silage diets due to the higher content of unsaturated fatty acids in pasture. This difference, however, is masked by the addition of high level of unsaturated fat from the rape seed. The CLA in milk from the rape seed fed animals fit nicely with the level expected from the sunflower experiment. The higher level of CLA in milk from the maize silage than the grass silage fed cows also related fairly well to the amount of trans-11 content in milk.

    The high level of trans-10 correspond to a significant increase in trans-10- cis- 12 CLA in milk (0.014 vs 0.029; P<0.01). In the comparable treatment in the experiment comparing rape seed with sunflower cakes the levels of both CLA and trans fatty acids were similar, but the amount of trans-10, cis-12 C18:1 was below the detection limit. The amount of trans fatty acids and CLA in the milk from the cows in Experiment 3 supports the notion that the unsaturated fatty acids from the sunflower cakes unfortunately were not absorbed.

    Besides these experiments we have conducted a number of trials in private and experimental herds (Nielsen et al., 2005b). The overall conclusions are in agreement with the literature. CLA in milk can be influenced by amount and source of fat in the diet, by forage type, by season and by breed (HF>Jersey). Furthermore there are consistent differences between cows on the same diet. Thus, it is possible to produce milk with elevated level of CLA if the consumers demand it.


    ω-3 fatty acids


    The level of ω-3 fatty acids in milk fat can be increased by using fresh grass due to its high content of α-linolenic acid (Chilliard and Ferlay, 2004). Of the vegetable fat supplements only linseed provides high level of α-linolenic acid and use of linseed can raise the level of ω-3 fatty acids in milk. Unfortunately the content of ω-3 fatty acids is reduced by conservation, but we did see a significant higher level of ω-3 fatty acids in the milk from the cows fed grass silage compared with maize silage (6.4 vs 3.9 mg/g FA; P<0.001) (Nielsen et al., 2006). The ω-3 content of C20 and C22 can be raised by fish oil or other marine feed sources in the diet (Chilliard et al., 2001).


    Conclusions


    In conclusion it is possible to improve the ratio of unsaturated to saturated fatty acids in milk fat and the levels of CLA and ω-3 fatty acids can also be raised. These effects are all considered favourable in connection with the human health


    effects attributed to milk fat. However, it is impossible to improve the level of one component without also affecting the others, and most importantly the effects cannot be obtained without a concomitant increase in the level of trans fatty acids. A raise in trans-11 is considered safe. We have data from a human invention trial that support this (Raff et al., 2006; Tholstrup et al., 2006). However, the effect of trans-10 is less certain. This is unfortunate because, as illustrated by our experiments, the content of trans-10 in milk fat can be very high especially when lipid supplementation is given together with maize silage/high starch diets.


    CORRELATED RESPONSES


    The previous section shows that it is possible to obtain a more favourable milk composition through dietary mean. However, it is important to realize that the diets that most effectively improve the milk fat composition also can have other correlated effects.

    One aspect is reduced de novo milk fat synthesis. In fact the increase in the observed relative content of unsaturated fatty acids in the milk fat is to a great extent achieved by a reduction in de novo milk fat synthesis caused by the addition of high levels of unsaturated fatty acids to the diet. Such diets, especially when containing high levels of concentrate, lead to a reduction of de novo milk fat synthesis (Bauman et al., 2006). This also occurred in our experiment. In the experiment with increasing amount of sunflower the relative amount of fatty acids with chains length below 16, reflecting de novo synthesis, was decreased from 33 to 21%, as a result of more than 30% reduction in the daily production of <C16 fatty acids (P<0.001) The result of feeding diets with high level of unsaturated fatty acids in combination with high level of concentrate - or maize silage with high starch content - usually is a decrease in the overall milk fat percentage. This is confirmed in the two other Experiments 2 and 3 (Nielsen et al., 2006; Sejrsen and Schaltz, unpublished). Interestingly, in the Experiment 1 with increasing sunflower the reduction in de novo synthesis was compensated by an increased in the uptake of preformed fatty acids such that daily total milk fat production remained the same. However, in the other experiments, with high fat supplementation, the reduction in de novo synthesis was reflected in a much lower milk fat content (Table 2).

    The mechanism of action behind the milk fat depression - or more precisely

    - the inhibition of de novo milk fat synthesis in the mammary gland - caused by feeding high level of unsaturated fat and starch involve inhibitory effects of the fatty acids produced during rumen biohydrogenation. It has been proven that trans-10, cis-12 CLA reduces mammary lipogenesis, but this isomer cannot alone explain all the reduction (Baumgard et al., 2001; Griinari and Bauman, 2006). However, the other factors are unknown, but it has been shown that trans-10 C18:1 does not cause reduction in mammary lipogenesis (Lock et al., 2007).


    It has furthermore been shown that dietary fatty acids can lead to inhibition of the expression of the genes coding for enzymes central for regulation of milk fat synthesis; acetyl CoA carboxylase and fatty acid synthase (Bernard et al., 2006). Recently attention has focused on sterol response element binding protein-1 (SREBP-1), a factor thought to play a key role in the overall regulation of lipogenesis. We have also studied the expression of these genes. Our results (Figure 1) also show that the expression of the genes related to mammary lipogenesis was reduced in cows having reduced milk fat synthesis (Sejrsen, Bjørn, Schaltz, Theil and Sørensen, unpublished).


    image

    image

    image

    image


    image

    image

    image

    image

    image

    image


    image

    image

    image

    image

    Figure 1. The effect of increasing level of sunflower seeds on the expression genes coding for enzymes involved in regulating milk fat synthesis. ACC- acetyl CoA caboxylase (P<0.05), FAS- fatty acid synthase (P<0.05), SREBP - sterol response element binding protein-1 (P<0.05) (Sejrsen, Bjørn, Schaltz, Theil and Sørensen, unpublished)


    Other important aspects relate to feeding the high amounts of unsaturated fatty acids required to changes fatty acid composition. First of all, it is important to consider the possible content of anti-nutritional compounds present in some feed items, such as glucosinolates in rape seed, and gossypol and aflatoxin in cottonseed meal and other tropical oilseed meals. These anti-nutrients have the disadvantage that they or their degradation products can be transferred into the milk and act like toxicants. Thus the degradation products goitrin and thiocyanate from glucosinolates can produce goiter by impairing the iodine secretion into milk and its metabolism (Nørgaard and Hvelplund, 2003).

    It is also important to consider the effect of unsaturated fat on vitamin status. In Experiment 2 we observed that the unsaturated fatty acids caused a reduction in the amount of vitamin E in the milk (Table 5). The content was reduced more in milk from cows fed sunflower cakes than in milk from cows fed rapeseed cakes, due to the higher content of unsaturated fatty acids in oil from sunflower compared to oil from rape seed. However, addition of 1450 mg vitamin E (RRR-α-tocopherol) was able to prevent the reduction of the vitamin E level in the milk. These effects are likely to occur in the rumen since the fatty acids from the sunflower diet, as mentioned, most likely were absorbed from the gut (Jensen et al., 2005).


    image

    Table 5. Concentration of α-tocopherol in milk from cows fed rape seed or sunflower meal with or without a daily supplement of 1450 mg RRR-α-tocopherol on top of diets containing 300 mg all-rac-α-tocopheryl acetate and sunflower or rapeseed cake1


    Group

    Vitamin E Date

    300

    0.47

    0.40

    0.35

    1750

    0.45

    0.61

    0.82

    300

    0.41

    0.27

    0.15

    1750

    0.49

    0.61

    0.61

    mg initial 1 week 5 week


    Rape seed


    Sunflower


    P NS * *

    1,2 adapted from Jensen et al. (2005); * - P<0.05


    Finally, it is also important to take other milk quality aspects into consideration. These include technological aspects, such as shelf life and spreadabilty, as well as sensory aspects, such as taste, aroma and flavour. These aspects are not covered in this presentation. The readers are referred to the review by Chilliard and Ferlay (2004) to get a lead to this aspect.


    OVERALL CONCLUSION


    The results discussed show that the prospects for obtaining a favourable milk fat composition of cow’s milk through dietary means are good. It is clear from the data that it is possible to reduce the relative amount of saturated fatty acids and increase the relative amount of unsaturated fatty acid by using elevated amounts of unsaturated fatty acids in the diet. The milk fat content of CLA can be increased in the same way and the amount of ω-3 fatty acid can also be increased, especially by using fresh grass in the diet. Unfortunately the same diets lead to an increase in milk fat content of trans fatty acids that are suggested having unfavourable effects on human health. However, trans fatty acids in milk have been considered without negative effect because most of the trans fatty acids in milk usually are trans-11. However, when the basal diets are high in starch, the content of trans-10 can be very high. The importance of this for human health is not known.

    Diets required to obtain the favourable milk fat composition have other effects that need to be taken into consideration. These include milk fat depression, vitamin E status, the risk of anti-nutritional factors in the fat sources and last, but not least, the technological and sensory quality of the milk and milk products.


    REFERENCES


    Bauman D.E., Griinari J.M., 2003. Nutritional regulation of milk fat synthesis. Ann. Rev. Nutr. 23, 203-227

    Bauman D.E., Lock A.L., Corl B.A., Ip C., Salter A.M., Parodi P.W., 2006. Milk fatty acids and humane health: potential role of conjugated linolic acid and trans fatty acids. In: K. Sejrsen, T. Hvelplund, M.O. Nielsen (Editors). Ruminant Physiology. Wageningen Academic Publishers, Wageningen (The Netherlands), pp. 529-561

    Baumgard L.H., Sangster J.K., Bauman D.E., 2001. Milk fat synthesis in dairy cows is progressively reduced by increasing supplemental amounts of trans-10, cis-12 conjugated linoleic acid (CLA). J. Nutr. 131, 1764-1769

    Bernard L., Leroux C., Chilliard Y., 2006. Charaterisation and nutritional regulation of the mail lipogenic genes in the ruminant lactating mammary gland. In: K. Sejrsen, T. Hvelplund, M.O. Nielsen (Editors). Ruminant Physiology. Wageningen Academic Publishers, Wageningen (The Netherlands), pp. 295-326

    Chilliard Y., Ferlay A., 2004. Dietary lipids and forages interactions on cow and goat milk fatty acid composition and sensory properties. Reprod. Nutr. Develop. 44, 467-492

    Chilliard Y., Ferlay A., Doreau M., 2001. Effect of different types of forages, animal fat or marine oils in cow‘s diet on milk fat secretion and composition, especially conjugated linoleic acid (CLA) and polyunsaturated fatty acids. Livest. Prod. Sci. 70, 31-48

    Chilliard Y., Ferlay A., Mansbridge R.M., Doreau M., 2000. Ruminant milk fat plasticity: nutritional control of saturated, polyunsaturated, trans and conjugated fatty acids. Ann. Zootech. 49, 181- 205

    Dewhurst R.J., Shingfield K.J., Lee M.R.F., Scollan N.D., 2006. Increasing the concentrations of beneficial polyunsaturated fatty acids in milk produced by dairy cows in high-forage systems. Anim. Feed Sci. Tech. 131, 168-206

    Griinari J.M., Bauman D.E., 1999. Biosynthesis of conjugated linolic acid and its incorporation into meat and milk in ruminants. In: M.P. Yurawecz, M.M. Mossoba, J.K.G. Kramer, M.W. Pariza G.J., Nelson (Editors). Advances in Conjugated Linolic Acid Research. AOCS Press, Champaign, Illinois. Vol. 1, pp. 180-200

    Griinari J.M., Bauman D.E., 2006. Milk fat depression: concepts, mechanisms and management applications. In: K. Sejrsen, T. Hvelplund, M.O. Nielsen (Editors). Ruminant Physiology. Wageningen Academic Publishers, Wageningen (The Netherlands), pp. 389-417

    Jenkins T.C., McGuire M.A., 2006. Major advances in nutrition: Impact on milk composition. J. Dairy Sci. 89, 1302-1310

    Jensen R.G., 2002. The composition of bovine milk lipids: January 1995 to December 2000. J. Dairy Sci. 85, 295-350

    Jensen S.K., Kristensen N.B., Lauritsen C., Sejrsen K., 2005. Enrichment of cows‘ milk with natural or synthetic vitamin E. 10th Symposium: Vitamins and Additives in Nutrition of Man and Animal. Jena/Thuringia (Germany), pp. 78-83

    Lock A.L., Tyburczy C., Dwyer D.A., Harvatine K.J., Destaillats F., Mouloungui Z., Candy L., Bauman D.E., 2007. Trans-10 octadecenoic acid does not reduce milk fat synthesis in dairy cows. J. Nutr. 137, 71-76

    Moorman P.G., Terry P.D., 2004. Consumption of dairy products and the risk of breast cancer: a review of the literature. Amer. J. Clin. Nutr. 80, 5-14

    Mozaffarian D., Katan M.B., Ascherio A., Stampfer M.J., Willett W.C., 2006. Medical progress - Trans fatty acids and cardiovascular disease. N. Engl. J. Med. 354, 1601-1613


    Nielsen T.S., Andersen R.H., Sørensen M.T., Weisbjerg M.R., Straarup E.M., Sejrsen K., 2005a.

    Conjugated linoleic acid (CLA) and vaccenic acid in Danish milk - influence of feeding and other production related factors (in Danish). DJF Raport 64, pp. 73

    Nielsen T.S., Straarup E.M., Sørensen M.T., Sejrsen K., 2005b. Increasing amounts of sunflower seeds increase CLA and vaccenic acid content in milk fat from dairy cows. 56th EAAP Annual Meeting. Uppsala (Sweden). Book of Abstracts. 11, 135

    Nielsen T.S., Straarup E.M., Vestergaard M., Sejrsen K., 2006. Effect of silage type and concentrate level on conjugated linoleic acids, trans-C18:1 isomers and fat content in milk from dairy cows. Reprod. Nutr. Develop. 46, 699-712

    Nørgaard P., Hvelplund T., 2003. Anti-nutritional factors and unwanted components in feedstuffs and poisoness plants (in Danish). In: T. Hvelplund, P. Nørgaard (Editors). Cattle Nutrition and Physiology. Raport 53, Vol.1, DJF, pp. 87-118

    Raff M., Tholstrup T., Sejrsen K., Straarup E.M., Wiinberg N., 2006. Conjugated linoleic acid (CLA) and vaccenic acid (VA) have no effect on blood pressure and isobar arterial elasticity in healthy young men. FASEB J. 20, A1016

    Tholstrup T., Raff M., Basu S., Nonboe P., Sejrsen K., Straarup E.M., 2006. Effects of butter high in ruminant trans and monounsaturated fatty acids on lipoproteins, incorporation of fatty acids into lipid classes, plasma C-reactive protein, oxidative stress, hemostatic variables, and insulin in healthy young men. Amer. J. Clin. Nutr. 83, 237-243

    Williams C.M., 2000. Dietary fatty acids and human health. Ann. Zootech. 49, 165-180

    Journal of Animal and Feed Sciences, 16, Suppl. 1, 2007, 21–41


    The prospect of obtaining beneficial mineral and vitamin contents in cow’s milk through feed


    C. Swensson1,2 and H. Lindmark-Månsson1


    1Swedish Dairy Association Scheelevägen 18, SE-223 63 Lund, Sweden

    2Unit of Rural Buildings and Animal Husbandry,

    Faculty of Landscape Planning, Horticulture and Agricultural Science, Swedish University of Agricultural Sciences

    P.O. Box 59, SE-230 53 Alnarp, Sweden


    ABSTRACT


    The dairy industry is searching for add-values in milk that will promote the sale of milk. Several minerals and vitamins are important in this aspect. One easy way of improving milk quality is to change dairy cow diet. The concentration of selenium and iodine is greatly influenced by dairy cow diet. Both vitamin A and E concentrations in milk can be altered by dairy cow diet. Preferable diets are pasture and/or high-quality forage. Most important for rumen synthesis of vitamins of the B- complex are a well-functioning rumen, which means feed consisting of high quality forage.


    KEY WORDS: dairy production, cow diet, milk quality, human health


    INTRODUCTION


    Milk is one of the essential foods representing an important part of the human diet. It is an excellent source of protein and calcium and also of many vitamins and trace elements, such as zinc, selenium and iodine. The composition of cow’s milk is of great importance for the dairy industry. It is fundamental for the value of milk and affects its nutritional value as well as its processability. Factors influencing the composition of milk are internal factors, e.g., the breed of cow, and external factors, such as type of feed, seasonal changes, milking frequency and milking systems. New techniques in milk production and dairy plants, and also new dairy products, will place new demands on milk composition.


    image

  2. Corresponding author: e-mail: christian.swensson@ltj.slu.se


There is also a need to “redesign” milk, the main reason being that milk is expensive to produce, both in economic and energetic terms, compared with vegetable products (Boland et al., 2001).

The focus must be on the specific value of milk. One important aspect is its health value. Examples are milk as a source of calcium and several vitamins such as vitamins A and E. The aim of this review is to elucidate the prospect of obtaining favourable mineral and vitamin contents in cow’s milk through feeding. Selected minerals and vitamins have been studied due to their possibility to improve the nutritional value of milk.


WHAT ARE FAVOURABLE MINERAL AND VITAMIN CONTENTS IN MILK?


The nutritive value of milk has long been recognized. The nutritional role of milk as a component of the human diet has traditionally been evaluated based on its overall contribution of essential and non-essential nutrients to a high-quality diet to promote growth and development (Huth et al., 2006). It is becoming increasingly evident that foods naturally containing high levels of nutrients, such as milk and other dairy products, improve bone growth and can


Table 1. The contributions of nutrients from major animal groups, per capita per day, and expressed as a percentage of the total in the US food supply (modified from Beitz, 2005)



Nutrient


meat, poultry

and fish

Animal food group dairy products


eggs


Total from animal foods

1970

2000

1970

2000

1970

2000

1970

2000

Vitamin A

36.0

27.0

21.8

22.1

6.7

5.3

64.5

54.4

Carotene

0.0

0.0

3.3

2.1

0.0

0.0

3.3

2.1

Vitamin E

5.4

4.0

3.9

2.4

3.4

1.9

12.7

8.3

Vitamin C

2.4

2.0

4.2

2.5

0

0

6.6

4.5

Thiamin

25.1

17.5

8.9

4.7

1.3

0.7

35.3

22.9

Riboflavin

21.6

16.7

38.4

26.3

9.5

6.1

69.5

49.1

Niacin

43.9

35.7

2.2

1.2

0.1

0.1

46.2

37.0

Vitamin B6

38.2

34.7

12.1

8.7

2.9

1.9

53.2

45.3

Folate

9.8

2.7

9.1

2.6

9.1

2.6

7.0

1.8

Vitamin B12

73.3

75.2

20.3

20.3

4.5

4.3

98.1

99.8

Calcium

2.8

3.2

75.6

72.2

2.3

1.8

80.7

77.2

Phosphorus

25.6

24.8

36.7

32.7

5.3

3.8

67.4

61.3

Magnesium

12.8

12.6

20.8

15.8

1.3

0.9

34.9

29.3

Iron

22.7

15.6

2.4

1.9

4.0

2.2

29.1

19.7

Zinc

46.9

37.8

19.4

16.8

3.9

2.6

10.2

57.2

Potassium

16.6

16.8

23.7

18.1

1.5

1.1

41.8

36.0

Selenium

18.4

28.1

16.2

10.9

10.5

6.1

45.1

45.1

Sodium 24.7 19.3 25.9 32.8 4.0 3.3 54.6 55.4


reduce the risk of other chronic diseases. In the United States the contribution from dairy products to the American diet regarding minerals and vitamins is of great importance (Table 1). In Sweden, the contribution from dairy products is of importance regarding vitamin A (11% of intake), vitamin D (15%), thiamine (13%), vitamin B12 (16%) and vitamin B6 (8%) (Table 2).


Table 2. The contributions of nutrients from dairy products, per capita per day, and as a percentage of the total in the Swedish food supply (modified from Riksmaten, 1997-1998)


Milk and yoghurt

Milk, yoghurt and cheese

Vitamin A

11

16

Carotene

1

3

Vitamin E

2

5

Vitamin C

0

0

Thiamin

13

14

Riboflavin

29

35

Niacin

9

14

Vitamin B6

8

9

Folate

13

15

Vitamin B12

16

22

Calcium

40

61

Phosphorus

23

34

Magnesium

13

16

Iron

1

2

Zinc

12

22

Potassium

15

16

Selenium

14

17


Beitz (2005) concluded that dairy products are one of the best sources of cal- cium, and that the content of iron and vitamin E should be increased in milk in order to contribute in a more complete way to human needs. Designer milk also offer the opportunity of new products (Boland et al., 2001). Hermansen et al. (2003) empha- sized the importance of carotenes and tocopherols as antioxidants. These compo- nents contribute to the quality of milk fat. In the Nordic Nutrition Recommendations for 2004 (NNR, 2005) recommended daily intakes are given for 9 minerals and trace elements and 10 vitamins. Before changing the content of minerals and vitamins in milk the consequences on milk quality should be considered.


FEEDING FOR A HIGH CONTENT OF MINERALS AND VITAMINS


Minerals and trace elements


Values of the concentrations of minerals and trace elements reported in the literature show a wide variation (Renner et al., 1989). The reason for this is that


levels are influenced by a variety of factors, including stage of lactation, season, nature of the soil, cattle, breed, feed and contaminants. Also, analytical errors have led to exceptionally high values of the concentrations of some trace elements, e.g., iodine, caused by the use of iodophores as udder disinfectants (Rasmussen et al., 1991). The chemical form of a nutrient is important because it may influence intestinal absorption and utilization and thus bioavailability. In Table 3 the absorption coefficients for dairy cows are summarized. Generally, nutrients that occur in a free form, such as soluble ions, are well absorbed, whereas those that are bound are often poorly absorbed.


Macro-minerals


Calcium. Over 90% of the Ca in the body is found in the teeth and bones where it is present as calcium phosphate (Flynn and Cashman, 1997). The content of Ca is approximately 1000 g in an average women and 1200 g in an average man (NNR, 2005). The remainder is present as an easily exchangeable pool in blood, extra-cellular fluid, and in the cells of the body. This free Ca plays a vital role in signal transduction, both within and between cells, in neuromuscular transmission, glandular secretion and in a large number of enzymatic reactions. Maintenance of a constant concentration is therefore of vital importance, and calcium homeostasis is probably the most highly regulated homeostatic mechanism. Ca is regarded as the most important mineral with respect to bone health. However, according to Cashman (2006), the exact relationship between Ca and bone health is not fully understood. In cow’s milk 99% of the Ca is in the skim milk fraction (Flynn and Cashman, 1997). Two-thirds of the total Ca is found in the colloidal form associated with the casein micelles, either as calcium phosphate (about half of the total milk calcium) or as calcium ions bound to phosphoserine residues (about one-sixth of the total calcium). The remaining one-third is soluble. Ionized Ca in the soluble phase accounts for about 10% of the total Ca. A small amount of calcium (0.15%) is bound to α-lactalbumin. The bioavailability of Ca in milk is high (Guéguen and Pointillart, 2000). The mean Ca absorption from cow’s milk by healthy human adults has been reported to range from 21 to 45% (Table 3). Some components in milk such as lactose and phosphopeptide may enhance calcium absorption. The Ca in milk and other dairy products is absorbed much better than the Ca in spinach or watercress as these plants have high oxalate contents.

Dairy cow diet has relatively little effect on the concentration of Ca in milk because the skeleton of the cow acts as a reservoir of minerals. Plasma Ca is given high priority even with serious deficiencies (NRC, 2001). The homeostatic regulation of both Ca and P and the reservoirs of these minerals in the skeleton make it difficult to alter the concentrations of Ca and P in milk by altering dairy cow diet or by changing feeding strategy. Kamiya et al. (2005) compared a low-


Table 3. Absorption coefficients for cows for macro- and trace minerals

image

image

Minerals Absorption coefficients for cows

Calcium

Forage1

0.30

Concentrates1 0.60

Phosphorus USA; Forages1 0.64

USA; Concentrates1 0.70

Denmark2 0.55

France2 0.60

The Netherlands2 0.60

Magnesium Natural feedstuffs1 0.16

Iron All feed1 0.10

Zinc All feed1 0.10

Potassium All feed1 0.90

Selenium All feed1 0.40-0.65

All feed2 0.30-0.65

Sodium All feed1 0.90

Chloride All feed1 0.90

image

1 NRC (2001), 2 Aaes et al. (2003)


calcium diet (0.43% Ca) with a high-calcium diet (0.86% Ca) three weeks before parturition and found no difference in Ca content in the colostrum or milk. Breed is probably more important than the cow’s diet: Jersey cows have a higher Ca concentration in milk than Holstein-Friesian cows (Knowles et al., 2006).


Phosphorus. P is abundant in the body, the largest amounts being found as hydroxyapatite in bones (NNR, 2005). It occurs as organic and inorganic phosphates in all body tissues and fluids, is an essential component of many biological molecules, including lipids, proteins, carbohydrates and nucleic acids, and plays a central role in the metabolism (Flynn and Cashman, 1997). Of the P in milk, 20% is found in ester linkages with the hydroxyl groups of serine and threonine residues of the caseins, 40% in inorganic phosphate in casein micelles and the remainder in lipids and water-soluble esters (Renner et al., 1989). Feed has relatively little effect on the concentration of P in milk for the same reason as Ca: the skeleton acts as a reservoir of minerals. The feeding of P to dairy cows has been questioned, due to concerns regarding eutrophication of the environment. The P feeding norm has been decreased in the USA, the Netherlands, Germany, Denmark and Sweden during the past decade (Aaes et al., 2003; Spörndly, 2003; Pfeffer et al., 2005). High-yielding cows often have problems associated with overfeeding of P (Aaes et al., 2003; Pfeffer et al., 2005). However, the concentrations of P in milk from 1970 compared to P in milk from 1996 did not increase during this period (Lindmark-Månsson et al., 2003).


Magnesium. According to Cashman (2003) there is little evidence of dietary deficiency of magnesium in human beings, except in serious diseases. In dairy


cows, Mg is important for several functions such as muscle function, nerve conduction and, together with P and Ca, bone mineral formation. Mg is also a cofactor in several metabolic pathways (NRC, 2001). In contrast to Ca and P, maintaining normal values of Mg in the blood plasma of dairy cows is almost totally dependent on the absorption of dietary Mg (NRC, 2001). However, it is difficult to alter the concentration in bovine milk by altering dairy cow diet. In cow´s milk 98-100% of the magnesium is in the skim milk phase, where 65% of the magnesium is in a soluble form (40% as magnesium citrate, 7% as magnesium phosphate and 16% as free magnesium ion), while the remainder is colloidal and is associated with the casein micelle.


Potassium. The major proportion of potassium in the body (90%) is found in the cells, and K is quantitatively the most important intracellular cation (NNR, 2005). Extra-cellular potassium, which constitutes the remaining 2%, is important for the regulation of the membrane potential of the cells, and thus nerve and muscle function. The important role of K in regulating blood pressure, in both the general population and in people with high blood pressure, has been demonstrated repeatedly in epidemiological as well as clinical studies, and is today well established (Vaskonen, 2003). K in milk is entirely soluble, completely ionic and fully available for absorption (Renner et al., 1989). Together with sodium and chloride, this monovalent ion is among the most prevalent minerals in milk (Atkinson, 1995). Major changes in the concentration of the major monovalent cations in milk, such as K, are associated with conditions that promote opening of the membranes between epithelial cells (Atkinson, 1995). As for Mg, the dairy cow is dependent on daily intake of K. However, the concentration in milk is rather constant, even if the daily intake of K fluctuates (NRC, 2001). Overfeeding dairy cows with K has a detrimental effect on the absorption of Ca and Mg.


Sodium and chloride. Na is the most important cation in extracellular fluids and regulates the osmolarity, acid-base balance and the membrane potential of cells. Chloride is the most important anion in extracellular fluid and is very important in the maintenance of fluid and electrolyte balance (Cashman, 2003). There is normally no dietary deficiency of Na or Cl in humans. On the contrary, there is probably a need in the Western world to decrease the intake of salt (NaCl) because of its influence on hypertension (von Wowern, 2006).

In summary; it would be beneficial for human nutrition to increase the concentration of Ca and K in bovine milk, but it seems to be difficult or impossible due to physiological reasons. Regarding P, there is no great advantage in increasing the concentration in milk and it is difficult to influence the concentration in dairy cow milk by altering the dairy cow diet. Due to environmental reasons it is more important to decrease the concentration of P in dairy cow diet as much as possible. Overfeeding dairy cows with P means more P in manure and environmental


problems. Increasing Mg in milk probably has no positive effect on humans and it is also difficult to influence the content in milk by changing dairy cow diet. Finally, there is a great deal of evidence that the overall dietary intake of salt should be decreased, hence, there is no need to increase the concentration of sodium or chloride in milk.


Trace elements


Fourteen trace elements are considered essential to humans, three of which are of special interest, namely selenium, iodine and iron, due to their positive effects on human health and the possibility of influencing the content in milk by changing dairy cow diet.


Selenium. Most of the Se in both human and bovine milk is protein bound (Debski et al., 1987). In bovine milk 60-80% of the Se is associated with the caseins, 20-40% with the whey proteins and 10-25% with the low-molecular fraction. Se occurs mainly as the amino acids selenocysteine and selenomethionine, which differ from cysteine and methionine in having a Se atom in place of the sulphur atom.

Selenium amino acids are principal dietary forms of the element available to free-living animals, but Se is often supplied in inorganic form in experimental diets and in supplements (Levander and Burk, 1996). Its chemical form in foods, the presence of other food constituents and the physiological status of the individual influence the bioavailability of Se. This has been studied mainly in animals, and only a few studies have been performed on man (Mutanen et al., 1986; Fairweather-Tait, 1997).

The dietary level of antioxidants, e.g., vitamins C and E, methionine and total protein may enhance Se bioavailability (Levander, 1991). Se is very well absorbed from milk, as demonstrated in subjects having undergone ileostomy (Chen et al., 2004). The amount of Se in milk is, however, influenced by other factors, such as the form and bioavailability of Se in the diet, as well as interactions with other nutrients. A value of 18 µg kg-1 in Swedish bulk milk was reported in 1996 (Table 4). The Se content in Swedish milk increased by approximately 80% from the early 1970s up to 1996, probably due to the increased addition of Se in dairy cow feed. It is possible to change the content of Se in cow’s milk by feeding. However, the uptake of Se by dairy cows differs depending on the source. Feeding with inorganic Se is not as efficient as feeding with organic selenium. With respect to the use of different forms of Se in food, yeast was found to be more effective than selenite in increasing the Se content in maternal serum and milk (Kumpulainen et al., 1985). Similarly, the transfer of dietary Se into bovine milk was found to be markedly more efficient with selenized yeast than when using sodium selenite as


a feed supplement (Knowles et al., 1999; Ortman and Pehrson, 1999). According to Givens (2004) the uptake of selenized yeast was 3-5 times higher than inorganic selenium. In another experiment 10-18% of the selenium given in dairy cow diet was found in the milk (Juniper et al., 2006). The same study also indicated that high levels of Se in the cows’ milk had no negative effects on other important components of milk. Se has also been administered to cows to minimize the oxidation of milk fat (Nicholson et al., 1991). Especially with vitamin E there is an interaction with Se as antioxidants (Christensen et al., 2006). This interaction is rather complicated and can be synergetic or antagonistic. Se is potentially the most poisonous essential trace mineral to animals. The US Food and Drug Administration have set an upper limit on Se in milk, 14 µg/L (Weiss, 2005; Christensen et al., 2006). Within EU, there is no upper limit in milk, although 20

µg/L has been suggested in Finland (Givens et al., 2004). Another problem with EU legislation, only inorganic feed additives (sodium selenite and sodium selenate) are allowed and, hence, not selenized yeast is allowed (Givens et al., 2004). The content of Se in milk is influenced by regional differences, i.e. the Se status of the soil. Interesting findings have been made in Finland, where the Se content of milk was doubled in a short time, by increasing the level of Se in mineral fertilizer (Ekholm et al., 1993; Syrjäla-Qvist and Aspila, 1993). In a Swedish comparison between organic and conventional milk a lower level of Se was found in organic milk (Toledo et al., 2002). In a similar Danish investigation no difference was found in Se concentration with different production systems (Hermansen et al., 2005). In Table 4 values of Se content in feed and milk and recommendations for daily intake for dairy cows are presented. To our knowledge, there is no obvious reason for the difference in Se norms between different countries.


image

Table 4. Concentrations of selenium and iodine in selected feed and milk and recommended daily intake for dairy cows


Item


In feed Sweden mg/kg

Recommended daily intake for dairy cows


In milk

µg/100 g

mg/kg DM

Selenium

Roughage

0.02

Sweden

0.20

Sweden

1.81

Barley

0.01

Denmark

0.10

Denmark

3.02

Oatley

0.01

USA

0.30

Soya meal

0.19

Rapeseed meal

0.09


Iodine


Roughage


-


Sweden (Milking cows)


0.60


Sweden


14.01

Barley

0.3

Denmark

0.10

USA

23.02

Oatley

0.1

USA

0.30

Rapeseed meal 0.7

1Lindmark-Månsson et al. (2003); 2Larsson and Sehestad ( 2003); 3Pennington (1990)


Iodine. Iodine has long been recognized as an essential micronutrient for humans and animals (Saikat et al., 2004). The importance of I arises from the fact that it is a constituent of the thyroid hormones. These hormones are essential for normal growth and physical and mental development in animals and humans (Hetzel, 1998). I deficiency is the world’s most prevalent cause of brain damage. I is present in foods mainly as iodide and, to a lesser extent, covalently bound to amino acids (Brody, 1994). Iodide is rapidly absorbed by the gut and assimilated by the thyroid gland for use in producing thyroid hormones. The I present as part of amino acids, that is, as part of tyrosine, is somewhat less well absorbed (Hetzel, 1998). Once the need for thyroidal I has been met, the kidneys excrete excess I, so the urinary I output reflects the I intake. I absorption and utilization may also be affected by goitrogens, mainly sulphur-containing glucosides (NNR, 2005). These are dietary constituents occurring, for example, in cabbage, turnips and rapeseed, which may act as competitors for I, e.g., thiocyanates. Most of the I in milk (80- 90%) is in the inorganic form, mainly as iodide in the water-soluble fraction, while 5-13% is bound to proteins through either covalent bonds or loose physical associations, with less than 0.1% bound to fat (Cashman, 2003).

Iodine enters the cow’s diet from grass, concentrated feeds or from iodized salts (Table 4). The topsoil of the pastures on which the cows graze has been shown to make an important contribution to the I content in milk. There is a good relation between the content of I in dairy cow diet and the concentration of I in milk (Swanson et al., 1990).

Another possible source of I in milk is that which arises from the use of iodophores as disinfectants in dairy plants and as teat dips. I is the only trace element for which there have been suggestions of excessive amounts in cow’s milk (Cashman, 2003). Data from various countries on the I concentration in cow’s milk indicate mean values of 100-770 µg L-1 with a wide range of values from 20 to >4000 µg L-1 (Flynn and Cashman, 1997). In earlier studies, prior to 1970, I in milk rarely exceeded 100 µg L-1. In Sweden, the I content in milk was found to be 140 µg L-1 in 1996 (Lindmark Månsson et al., 2003).

The contents of I in Swedish dairy milk have increased by 75% compared with the investigation in 1973 (Swedish Dairy Association, 1973). A similar increase in I content has been observed in milk from the UK, from 15 µg 100 g-1 in 1991/1992 to

30.3 µg 100 g-1 in 1995, and in a follow-up investigation in 1998/1999 the content was found to be 31.1 µg 100 g-1 (UK Ministry of Agriculture, 2000). The I level in Irish milk is close to that found in milk in the UK (O´Brien et al., 1999). As for Se, there is a difference in I norms between different countries (Table 4).


Iron. Fe has several functions in the body; it is a component of heme found in myoglobin and haemoglobin, and it acts as cofactors of several enzymes such as catalase, cytochrome oxidase and ferredoxin (NRC, 2001). Fe is an important


trace element in humans, especially for women. During pregnancy clinical iron deficiency occur among as many as 20% of all women (MacRae et al., 2005; Knowles et al., 2006). Only a minor part of Fe in the human diet, 5-15%, is absorbed (Péréz et al., 2002). In dairy the industry, the Fe-binding glycoprotein in milk, lactoferrin, has been recognized due to various positive health effects (Wakabayashi et al., 2006).

On the other hand, Fe deficiency in adult cattle is unusual (NRC, 2001). According to Knowles et al. (2006) there are indications that it is possible to increase the concentration of Fe in milk by changing dairy cow diet. However, several obstacles must be overcome, such as the bioavailability of Fe and interactions with other chemical compounds (Knowles et al., 2006).


Zinc. Zinc has several important functions in humans. It is involved in the immune system and is essential for growth and development. Many hormones contain Zn, such as insulin and reproduction hormones (Cashman, 2003).According to Cashman (2003) there is a considerable difference in human absorption of Zn depending on the milk source. Zn from human milk is more easily absorbed than that in bovine milk. In Western countries milk and dairy products contribute 19- 31% of the total Zn intake. Zinc also has a positive effect on the immune system of cows (Lindmark-Månsson et al., 2000). Zn deficiency among dairy cows is probably not a serious issue in the Scandinavian countries (Aaes et al., 2003). However, a high uptake of copper or cadmium is antagonistic to Zn uptake. It is difficult to change the concentration of Zn in milk by altering the dairy cow diet. Lindmark-Månsson et al. (2000) reported that supplementing dairy cow diet with Zn prolonged the growth of starter cultures. Gustafson et al. (2007) report that the equipment in the cow shed is probably one source of Zn.


In summary; the concentrations of Se and I in milk are rather easy to alter by changing dairy cow diet. It would be desirable to increase the concentration of Fe in milk, but unfortunately this appears to be difficult at the moment. An increased content of Fe may also increase the oxidation in milk.


Vitamins


All known vitamins are found in milk (Renner et al., 1989). The relative contributions from cow’s milk to the human dietary requirements vary, but for some vitamins, particularly riboflavin (B2) and vitamin B12, milk is a particularly rich source.

The fat-soluble vitamins A, D, E and K, are, as their names imply, associated with the

fat fraction of the milk, whereas the water-soluble vitamins of the B complex and vitamin C are associated with the non-fat, aqueous fraction, or whey.


Fat-soluble vitamins. The concentrations of the fat-soluble vitamins A and E are dependent on the dietary intake of the cow and on the concentration of fat in the milk (Renner et al., 1989). Large seasonal variations are often seen in their concentration in milk. The vitamin D content is mainly influenced by the exposure of the animal’s body to ultraviolet light (Renner et al., 1989). Because of the large amount of vitamin K synthesized by ruminal and intestinal bacteria, it is also unlikely, that dietary vitamin K has much, if any effect, on the level in milk (NRC, 2001). The breed of cow also has a significant effect on the concentration of fat- soluble vitamins in milk: high-fat milk (from Jersey and Guernsey cows) has a higher content of vitamin E and ß-carotene, but a lower content of vitamin A due to a lower dioxygenase activity at the intestinal mucosa than milk from Friesian or Holstein cows. The yellow-orange colour of high-fat dairy products depends on the concentration of carotenoids, and hence on the diet of the animal. Carotenoids are not transported to the milk of goats and sheep, which is why their milk fat appear white compared to that of cows.

Vitamin A-carotenes. Vitamin A constitutes a group of chemically closely related compounds possessing the biological activity of retinol (Öste et al., 1997). Carotenes are precursors of retinol, i.e. vitamin A (Nozière et al., 2006b). Carotenes are a subgroup of the carotenoid family, which contains of more than 600 molecules and they are involved in the photosynthetic process. According to Nozière et al. (2006b), there are approximately 10 carotenoids in ruminant feeds, and the most important are β-carotene and lutein.

Vitamin A is essential to all vertebrates and has numerous important functions, for example, in vision, the maintenance of epithelial surfaces, immunodefence, growth, development and reproduction (NNR, 2005). Acute and chronic effects of vitamin A excess are well documented in the literature (Penniston and Tanumihardjo, 2006). Osteoporosis and hip fractures are associated with vitamin A intakes that are only twice the current recommended daily intake. The transfer of β-carotene from blood to milk seems to occur by passive diffusion (Jensen, 1995). The transfer of vitamin A from blood to milk is not determined by the vitamin A content of blood, presumably due to the strong regulation in the liver. Vitamin A is efficiently absorbed and utilized by humans at absorption rates of 70-90%. Carotenoids are absorbed much less efficiently, at rates of 20-50%, depending the individual’s vitamin A status and other non-dietary factors.

The vitamin A activity in milk does not depend solely on the vitamin as such, but also on carotenoids, of which β-carotene is by far the most important (Renner et al., 1989). Carotenoids are abundant in plant material and appear in milk as the result of their ingestion by the cow. β-carotene is found in vegetative material, hence forage is a good source of β-carotene, while grain and grain by-products contain very little or no β-carotene. β-carotene is easily oxidized and concentrations decrease quickly during storage (NRC, 2001). Investigations of the concentration


of vitamin A in roughage and concentrate show a considerable variation, thus indicating that vitamin values in feed tables are not reliable (Kristensen, 2003; Nadeau and Johansson, 2003). According to Nadeau and Johansson (2003) it is possible to retain the concentrations of β-carotene in silage if the silage is of high quality, the level of hygiene is good and the weather during harvest is sunny and dry. However, an investigation by Nozière et al. (2006a) shows a large difference in the concentration of β-carotene between silage and hay, the latter having a lower value. β-carotene is converted, to varying degrees, into vitamin A in the body.

Depending on the breed of cow and the carotenoid intake, the conversion of β-carotene into vitamin A, which occurs mainly in the intestinal mucosa, involves enzymatic conversion to retinal, which is then reduced to retinol. Thus retinol and hydrolysed retinyl esters from the feed are absorbed and re-esterified. Vitamin A is present in cow’s milk as retinol, retinol esters and carotene (Öste et al., 1997). In bulk milk the variation in retinol and carotenoid concentrations is reduced compared to the variation between and within the milk of individual cows. However, there are often seasonal and regional variations of retinol and carotenoid concentrations, which reflect the nature of the forage used (Nozière et al., 2006b). In Swedish dairy milk the retinol content was found to increase by over 30% from the winter months to the summer, from 30.7 µg/100 g in March to

40.7 µg/100 g in September (Lindmark Månsson, 2003).

Thus, to achieve a high concentration of β-carotene in milk, the importance of a cow diet with high-quality roughage, especially silage or pasture, cannot be underestimated. If the cow diet is supplemented with vitamin A, it is important to be aware that the destruction of vitamin A in the rumen can be high (NRC, 2001). In Sweden, low-fat milk is supplemented with both vitamin A and D. The goal is to achieve a concentrationof 25 µg vitamin A/100 g milk (www.mjolkframjandet.se, access 2006-11-19).


Vitamin E - tocopherols. Vitamin E has traditionally been used as a common term for two groups of components with biological vitamin E activity in mammals, tocopherols and tocotrienols, which are synthesized in plants (NNR, 2005). Vitamin E is essential for neurological function and acts as a lipid-soluble antioxidant. The vitamin E activity in plants is influenced by species, variety and stage of maturation, as well as by harvesting, processing and storage conditions (Morrissey and Kiely, 2003). The concentration of vitamin E in animal products is usually low, but such products may provide significant sources of this vitamin to humans because of their high consumption. In humans, vitamin E is taken up in the proximal part of the intestine, and uptake depends on the amount of food lipids, bile and pancreatic esterases that are present. It is emulsified together with fat-soluble components of the food. Lipolysis and emulsification of the lipid droplets formed then lead to the spontaneous formation of mixed micelles, which


are absorbed at the brush border membrane of the mucosa by passive diffusion. It is generally believed that the absorption of tocopherols is incomplete and that tocopherol esters need to be hydrolysed prior to absorption (Öste et al., 1997). The principal form of vitamin E in milk is α-tocopherol.

The vitamin E content of cow’s milk is rather low and it depends to some extent on the feed. Summer milk generally has higher concentrations than winter milk, as illustrated by findings in Swedish dairy milk where the lowest content of α- tocopherol, 92 µg 100-1 g, was found in February and the highest content, 110 µg 100 g –1, in July (Lindmark-Månsson, 2003). According to NRC (2001), the most biologically active form of vitamin E is α-tocopherol. There are eight different stereoisomers of vitamin E, RRR-α-tocopherol has the highest biological activity (NRC, 2001; Krogh-Jensen, 2005). This naturally occurring isomer also has the highest biological function compared to synthetic stereoisomers (Meglia et al., 2006). In a study by Bourne et al. (2007) comparing the effects of parental and oral administration of vitamin E to dairy cows on plasma and milk concentrations, they were actually comparing the administration of two different isomers. The positive effects in dairy cows are several. Vitamin E improves reproduction efficiency by decreasing the retention time of the foetal membranes and there is also evidence of a reduction in the incidence of mastitis (Baldi, 2005). The recommended intake for dairy cows has been increased over the past 10-15 years; NRC recommended 15 IU per kg DM in 1989 and today the recommendation is 80 IU/kg DM in the dry period and 20 IU/kg DM during lactation (Baldi, 2005). According to McDowell et al. (1996) there is a significant amount of vitamin E in whole cereal grains, especially in the germ and in by-products containing the germ. The main feed source of vitamin E is forage, especially fresh forage. Important factors affecting the concentration of vitamin E in forage are the stage of maturity and storage conditions. Silage is better than hay as storage losses from hay can be substantial (McDowell et al., 1996; NRC, 2001).


Water-soluble vitamins


The water-soluble vitamins of the vitamin B complex are synthesized by rumen bacteria and this is the main source of these vitamins in milk (Renner et al., 1989). Vitamin C is synthesized in the liver and possibly in the intestinal and kidney tissues.


B vitamins. The general belief, according to Schwab et al. (2006) is that “dietary supply and ruminal synthesis are sufficient to meet dairy cow requirements of B vitamins”. However, diets supplemented with biotin, thiamine, folic acid and vitamin B12 has been shown to have positive effects on lactation (Schwab et al.,

2006). The importance of microbial synthesis was demonstrated in an American


study where the apparent digestibility with different B-vitamins was investigated. The conclusion was that ruminal synthesis of B-vitamines was influenced by dietary forage and the non-fermentable carbohydrate (NFC) content of dairy cow diet. The highest amount of microbial synthesis was observed for niacin, riboflavin, B12, thiamin, B6, and folic acid. No biotin was found, either because

none was synthesized or because more biotin was destroyed by ruminal microbes

than synthesized (Schwab et al., 2006). It was also concluded that high forage content decreased ruminal apparent synthesis of folic acid and B12 , and increasing NFCs in dairy cow diet increased the ruminal apparent synthesis of niacin and B12. Several investigations have presented results indicating higher milk yield and/or increased concentration of different milk components when dairy cow diets are supplemented with different types of B vitamins. Supplementing dairy cow diet with biotin increases milk yield, according to Majee et al. (2003). In an investigation carried out by Jaster and Ward (1990) a cow diet supplemented with nicotinamide led to greater milk production and a higher percentage fat. On the other hand, Nielsen and Ingvartsen (2000) concluded in a review of several investigations regarding niacin administration to dairy cows that supplementary

niacin had no effect on milk production. However, there is little or no information on the influence of the concentration of B vitamins in milk, apart from folates and vitamin B12.


In an investigation of Swedish dairy milk, the content of all water-soluble vitamins, except biotin, showed a seasonal variation (Lindmark-Månsson et al., 2003). A possible explanation of this could be that the seasonal variation in the feed influences the synthesis of the ruminal microorganisms.


Folates. Folate is a generic term for a group of compounds that includes folic acid and derivatives having nutritional properties similar to folic acid (NNR, 2005). Folate is essential for one-carbon transfer reactions required in many metabolic pathways, including purine and pyrimidine biosynthesis (Öste et al., 1997). Folates serve as coenzymes and are required for normal cell division (NNR, 2005). One central folate-dependent reaction in amino acid metabolism is the remethylation of homocystein to methionine. The reaction requires vitamin B12. Homocystein is also removed by a reaction that requires vitamin B12. Food

folate must be hydrolysed by pancreatic and brush border folate conjugase to

monoglutamates prior to absorption in the upper part of the small intestine. It is difficult to summarize our knowledge concerning folate bioavailability in humans, because only a few studies have been carried out and they have given conflicting results (Witthöft and Jägerstad, 2003). In milk, the naturally occurring folate is bound to folate-binding proteins (Öste et al., 1997). According to Girard et al. (2005) folic acid is probably important for the prevention of several diseases such as disease and cardiovascular disease.


In dairy cows, requirements of folic acid and pantothenic acid cannot be met only by ruminal synthesis (NRC, 2001). Studies have also been presented indicating production and health benefits when dairy cow diets are supplemented with B vitamins (NRC, 2001). As mentioned above, there is an interaction between folic acid, methionine and vitamin B12. Girard et al. (2005) have shown that supplementary

folic acid increased crude protein and also casein concentrations in milk, however, if

the cows were fed rumen-protected methionine the effect of folic acid disappeared. Supplementation of dairy cow diet with folic acid or methionine increased the concentration of folic acid in milk.


Thiamin (B1). The predominant origin of thiamine in milk is biosynthesis in the rumen (Fox and McSweeney, 1998). Thus, thiamine concentration in milk is not considered to be influenced by feed, breed or season to any great extent, but the literature is inconsistent on these points. Shaver and Bal (2000) found

that supplementation with thiamine increased milk yield and milk fat and milk protein in two experiments and the opposite in a third experiment. They concluded that dairy cows on diets with a low fibre content and a high content of non-fibre carbohydrates given supplementary thiamine responded by an increase in milk yield. No information was given about the concentration of thiamine in milk.


Vitamin B12. Vitamin B12 is a common term for a group of cobalt-containing compounds, which are biologically active in humans (NNR, 2005). Vitamin B12 is unique among the vitamins in that it is the largest and most complex and because

it contains the metal ion, cobalt (Brody, 1994). Good dietary sources of vitamin B12 for humans are mainly animal-derived products, and vegan diets are thus almost devoid of vitamin B12 (Biesalski and Back, 2003). The major effect of B12 deficiency is growth impairment, particularly of rapidly growing cells, such as immature red blood cells, and macrocytic hyperchromic anaemia is a common symptom in both vitamin B12 and folate deficiency. Neurological disorders are also characteristic of vitamin B12 deficiency. Vitamin B12 deficiency is manifested years after the onset of nutrient imbalance or functional disorder, because the body pool is large.

Vitamin B12 is a cofactor for only two known human enzymes. The major proportion of vitamin B12 in foodstuffs is bound to a specific protein (Biesalski and Back, 2003). Absorption of vitamin B12 in humans is a multistep process (NNR, 2005). Protein-bound vitamin B12 in foods must be cleaved from the protein and absorption requires a glycoprotein, i.e. an intrinsic factor, secreted by the parietal cells of the stomach. The only natural source of vitamin B12 is microbes and, hence the predominant source of B12 for cows, and hence in milk, is biosynthesis by rumen microorganisms (Öste et al., 1997; NRC, 2001). The only time vitamin B12 deficiency could be expected in a cow with a well-functioning rumen is when the cow has a cobalt deficiency. Normally, feedstuffs from plants and animals will


contain enough cobalt. There are examples indicating that forage growing on soils with a low content of cobalt may contribute to vitamin B12 deficiency (NRC, 2001). In other words; the content of vitamin B12 in milk depends on the cobalt intake of the cow. According to Schwab et al. (2006), who investigated the apparent synthesis of B-vitamins, the most favourable dairy cow diet for vitamin B12 synthesis was 35% forage and 30% non fermented carbohydrates (NFC) in diet. Increasing the sugar content in the diet increased vitamin B12 synthesis. As mentioned, vitamin B12 supplementation of dairy cow diet increased vitamin B12 in milk by over 200% (Girard and Matte, 2005). Hydroxycobalamin is the predominant form of vitamin B12 in cow’s milk. Over 95% of the vitamin B12 in milk is protein bound.


Vitamin C. Ruminants from approximately the age of three weeks synthesize vitamin C. Vitamin C, or ascorbic acid, as it is also known, can function as an antioxidant (NRC, 2001). Changing the concentration of ascorbic acid in milk could affect the development of oxidized flavour in milk (Barrefors et al., 1995). In a trial involving supplemental dietary vitamin C, plasma concentrations of ascorbic acid increased, but this was not reflected by an increased concentration of ascorbic acid in milk (Weiss, 2001).


In summary; the fat-soluble vitamins A and E are correlated to the fat content in milk. Both vitamin A and E concentrations in milk can be altered by changes in dairy cow diet. Preferable diets are pasture and/or high-quality forage. The most important factors in rumen synthesis of B vitamins are a well-functioning rumen with both high-quality forage and easily soluble carbohydrates.


DISCUSSION


Finding a dairy cow diet or natural feeding that ensures the optimal milk quality regarding vitamin and mineral content could be simple or may involve a great deal of research. The simple answer is that the “natural” dairy cow diet is probably best in many ways. A dairy cow diet based on grass or pasture or both, provides a stable environment, which promotes the production of vitamin A and E and several B vitamins. Havemose et al. (2004) investigated the influence of type of roughage on the concentration of, for example, riboflavins, tocopherols, carotenes and luteins, and concluded that the concentrations of these components were higher in grass silage than in maize silage. This is probably also the explanation of the difference in the concentration of E vitamins in conventional and organic Danish milk reported by Nielsen (2005). However, one objection against the “natural” diet is that feed is produced on the farm. Home made feed, could have several shortcomings, for example, lack of Se or I, depending on the status of these trace minerals in the soil.


A great deal of research could be done to determine the most beneficial mineral and vitamin contents in milk. However, the macro-minerals Ca, P and Mg are in homeostasis with the skeleton, which acts as a reservoir of these elements, and it is a difficult to change their content in milk by changing dairy cow diet. A surplus of P is regarded as an environmental problem, and any efforts to raise the level in dairy cow milk should be undertaken with care. Na and Cl concentrations in milk are considered to be independent of dietary intake (Cashman, 2003). There is also evidence that the intake of salt is too high in the Western world and therefore levels of sodium and chloride in milk should not be increased. Normally, there is no dietary deficiency of the macro-minerals Na, Cl and K and hence, there is no great need to increase the content of these minerals in milk.

Regarding trace elements there is a lack of knowledge on the content in the dairy cow diet and in milk and, more importantly, of the bioavailability of these to both the cow and humans. According to Cashman (2003), Zn in human milk is more bioavailable than that in bovine milk.

However, when altering the content of vitamins and minerals in bovine milk it is necessary to assess the impact on the overall milk composition and implications on milk quality and processing.

Another aspect is how to change the dairy cow diet to achieve a favourable content of minerals and vitamins. At least in the Scandinavian countries this should be done by altering the feed components and not by parenteral methods, as proposed by Knowles et al. (2006). “Long-acting injectable and/or bolus supplements” are not the way forward. Dairy cows eating natural foods should produce healthy dairy products.


CONCLUSIONS


The concentrations of Se and I could easily be changed in a favourable way by altering dairy cow diet. However, there is a risk of an excess of these two trace minerals, especially Se. Also, vitamin A and E show a strong correlation with daily intake; a higher concentration of roughage and pasture in dairy cow diets promotes these vitamins. Organic dairy production is probably favourable with respect to vitamins. Such a diet also promotes a well-functioning rumen and therefore also the synthesis of B vitamins. However, when altering the content of vitamins and minerals in dairy cow milk it is necessary to assess the impact on the overall milk composition


REFERENCES


Aaes O., Sehested J., Larsen T., 2003. The requirements and support of vitamines to dairy cows (in Danish). In: Kvaegets ernaering og fysiologi . Bind 2 - Fodring og fysiologi. DJF Report Animal Husbandry No. 54. Faculty of Agricultural Sciences, Aarhus University (Denmark), pp.153-177

Atkinson S., Alston-Mills B., Lönnerdal B., Neville M.C., 1995. Major minerals and ionic constituents of human and bovine milks. In: R.G. Jensen (Editor). Handbook of Milk Composition. Academic Press, London

Baldi A., 2005. Vitamin E in dairy cows. Livest. Prod. Sci. 98, 117-122

Barrefors P., Granelli K., Appelqvist L.A., Bjoerck L., 1995. Chemical characterisation of raw milk samples with and without oxidative off-flavor. J. Dairy Sci. 78, 2691-2699

Beitz D.C., 2005. Contributions of animal products to healthy diets. In: Proceedings from Cornell Nutrition Conference for Feed Manufacturers. Cornell University, Ithaca, pp. 117-126

Biesalski H.K., Back E.I., 2003. Vitamin B12, nutritional significance. In: H. Roginski, J.W. Fuquay,

P.F. Fox (Editors). Encyclopaedia of Dairy Science. Academic Press, London, pp. 2721-2726

Boland M., MacGibbon A., Hill J., 2001. Designer milk for the new millennium. Livest. Prod. Sci.

72, 99-109

Bourne N., Wathes C., McGowaan M., Laven R., 2007. A comparison of the effects of parental and oral administration of supplementary vitamin E on plasma vitamin E concentrations in dairy cows at different stages of lactation. Livest. Sci. 106, 57-64

Brody T., 1994. Nutritional Biochemistry. Academic Press., London

Cashman K.D., 2003. Minerals in dairy products. In: H. Roginski, J.W. Fuquay, P.F. Fox (Editors).

Encyclopedia of Dairy Sciences. Academic Press, Bodmin, Cornwall (UK), pp. 2051-2065 Cashman K.D., 2006. Milk minerals (including trace elements) and bone health. Int. Dairy J. 16,

1389-1398

Chen J.H., Lindmark-Månsson H., Drevelius P., Tidehag G., Hallmans E., Hertervig E., Nilsson A., Åkesson B., 2004. Bioavailability of selenium from bovine milk as assessed in subjects with ileostomy. Eur. J. Clin. Nutr. 58, 350-355

Christensen B.T., Jörgensen V., Larsen T., Damgaard-Poulsen H., Strandberg M.T., Sörensen P., 2006. Selenium use in Danish agriculture (in Danish). DJF Report Soil Management No. 125, Faculty of Agricultural Sciences, Aarhus Universitet (Denmark)

Debski B., Picciano M.F., Milner J.A., 1987. Selenium content and distribution of human, cow and goat milk. J. Nutr. 117, 1091-1097

Ekholm P., Ylinen M., Varo P., 1993. Selenium content in milk during the selenium fertilization in Finland. Norwegian J. Agr. Sci., Suppl. 11, 211-213

Fairweather-Tait S.J., 1997. Bioavailability of selenium. Eur. J. Clin. Nutr. 51, Suppl 1, 20-23 Flynn A., Cashman K., 1997. Nutritional aspects of minerals in bovine and human milks. In: P.F. Fox

(Editor). Advanced Dairy Chemistry. Chapter 7. Lactose, Water, Salts and Vitamins. Chapman

& Hall, New York

Fox P., McSweeney P., 1998. Dairy Chemistry and Biochemistry. Kluwer Academic Plenum Publ., New York, London

Girard C.L., Lapierre H., Matte J.J., Lobley G.E., 2005. Effects of dietary supplements of folic acid and rumen-protected methionine on lactational performance and folate metabolism of dairy cows. J. Dairy Sci. 88, 660-670

Girard C.L., Matte J.J., 2005. Folic acid and vitamin B12 requirements of dairy cows: A concept to be revised. Livest. Prod. Sci. 98, 123-133

Givens D.I., Allison R., Cotrill B., Blake J.S., 2004. Enhancing the selenium content of bovine milk through altereration of the form and concentration of selenium in the diet of the dairy cow. J. Sci. Food Agr. 84, 811-817


Guéguen L., Pointillart A., 2000. The bioavailability of dietary calcium. J. Amer. Coll. Nutr. 19, 119- 136

Gustafson G., Salomon E., Jonsson S., 2007. Barn balance calculations of Ca, Cu, K, Mg, Mn, N, P, S and Zn in a conventional and organic dairy farm in Sweden. Agr. Ecosyst. Environ. 119, 160-170 Havemose M.S., Weisbjerg M.R., Bredie W.L.P., Nielsen J.H., 2004. The influence of feeding

different types of roughage on the oxidative stability of milk. Int. Dairy Sci. 7, 563-570

Hetzel B.S., 1998. Iodine-deficiency disorders. In: J.S. Garrow, W.P.T. James (Editors). Human Nutrition and Dietetics. Churchill Livingstone, London, pp. 534-555

Hermansen J.-E., Holm-Nielsen J., Bach-Larsson L., Sejrsen K., 2003. The quality and composition of milk (in Danish). In: F. Strudsholm, K. Sejrsen (Editors). Nutrition and Physiology of Cattle. Issue. 2 - Feeding and Physiology. DJF Report Animal Husbandry No. 54. Faculty of Agricultural Sciences, Aarhus University (Denmark), pp. 341-369

Hermansen J.-E., Badsberg J., Kristensen T., Gundersen V., 2005. Major and trace elements in organically or conventionally produced milk. J. Dairy Res. 72, 362-368

Huth P.J., DiRienzo D.B., Miller G.D., 2006. Major scientific advances with dairy foods in nutrition and health. J. Dairy Sci. 89, 1207-221

Jaster E.H., Ward N.E., 1990. Supplemental nicotinic acid or nicotinamide for lactating dairy cows.

J. Dairy Sci. 73, 2880-2887

Jensen R.G., 1995. Water-soluble vitamins in bovine milk. In: R.G. Jensen (Editor). Handbook of Milk Composition. Academic Press, pp. 688-692

Juniper D.T., Phipps R.H., Jones A.K., Bertin G., 2006. Selenium supplementation of lactating dairy cows: effect on selenium concentration in blood, milk, urine an feces. J. Dairy Sci. 89, 3544-3551 Kamiya Y., Kamiya M., Tanak M., Shioya S., 2005. Effects of calcium intake and parity on plasma

minerals and bone turnover around parturition. Anim. Sci. J. 76, 325-330

Knowles S.O., Grace N.D., Wurms K., Lee J., 1999. Significance of amount and form of dietary selenium on blood, milk, and casein selenium concentrations in grazing cows. J. Dairy Sci. 82, 429-437

Knowles S.O., Grace N.D., Knight T.W., McNabb W.C., Lee J., 2006. Reasons and means for manipulating the micronutrient composition of milk from grazing cattle. Anim. Feed Sci. Tech. 131, 154-167

Kristensen T., 2003. Strategies and challenge for organic milk production based on home grown feed (in Swedish). Konferens Ekologiskt Lantbruk Vägar-Val-Visioner. Proceedings CUL, SLU, pp. 127-131

Krogh-Jensen S., 2005. The support of vitamines in organic dairy production (in Swedish). In: C. Swensson (Editor). Natural Vitamines. Report No. 7052-P, Swedish Dairy Association, Lund (Sweden), pp. 6-7

Kumpulainen J., Salmenpera L., Simes M.A., Koivistoinen P., Perheentupa J., 1985. Selenium status of exclusively breast-fed infants as influenced by maternal organic or inorganic selenium supplementation. Amer. J. Clin. Nutr. 42, 829-835

Larsen E., Schestad J., 2003. Absorption and metabolism of minerals (in Danish). DJF report Animal Husbandry No. 53. Faculty of Agricultural Sciences, Aarhus University (Denmark), pp. 331-370

Levander O.A., 1991. Scientific rationale for the 1989 recommended dietary allowance for selenium.

Amer. Diet. Assn. 91, 1572-1576

Levander O.A., Burk R.F., 1996. Selenium. In: E.E. Ziegler, L.J. Filer (Editors). Present Knowledge in Nutrition. ILSI Press. Washington, DC, pp. 320-338

Lindmark-Månsson H., Fonden R., Pettersson H.-E., 2003. Composition of Swedish milk. Int. Dairy J. 13, 409-425


Lindmark-Månsson H., Svensson U., Paulsson M., Alden G., Frank B., Jonsson G., 2000. Influence of milk components, somatic cells and supplemental zinc on milk processability. Int. Dairy J. 10, 423-433

Majee D.N., Schwab E.C., Berics S.J., Seymour W.M., Shaver R.D., 2003. Lactation performance by dairy cows fed supplemental biotin and a B-vitamin blend. J. Dairy Sci. 86, 2106-2112 McDowell L.R., Williams S.N., Hidiroglou N., Njeru C.A., Hill G.M., Ochoa L., Wilkinson N.S.,

1996. Vitamin E supplementation for the ruminant. Anim. Feed Sci. Tech. 60, 273-296

McRae J., O’Reilly L., Morgan P., 2005. Desirable characteristics of animal products from a human health perspective. Livest. Prod. Sci. 94, 95-103

Meglia G.E., Jensen S.K., Lauridsen C., Persson-Waller K., 2006. Alpha-tocopherol concentration and stereoisomer composition in plasma and milk from dairy cows fed natural or synthetic vitamin E around calving. J. Dairy Res. 73, 227-234

Morrisey P.A., Kiely M., 2003. Vitamin E, nutritional significance. In: H. Roginski, J.W. Fuquay,

P.F. Fox (Editors). Encyclopaedia of Dairy Science. Academic Press, London, pp. 2670-2677 Mutanen M., Aspila P., Mykkanen H.M., 1986. Bioavailability to rats of selenium in milk of cows

fed sodium selenite or selenited barley. Ann. Nutr. Metab. 30, 183-188

Nadeau E., Johansson B., 2003. Important factors which influence on the content of vitamines in silage. Conference “Organic Production, Proceedings Centre of Sustainable Agriculture”. Swedish University of Agricultural Sciences (Sweden), pp. 137-141

Nicholson J.W.G., St-Laurent A.-M., McQueen R.E., Charmley E., 1991. The effect of feeding organically bound selenium and α-tocopherol to dairy cows on susceptibility of milk to oxidation. Can. J. Anim. Sci. 71, 135-143

Nielsen H.J., 2005. The influence of production methods on the content of pro/antioxidants in milk (in Danish). Workshop - Health and Organic Production Methods. Internal Report No. 59 (in Danish). Danish Centre for Organic Food and Farming (Denmark), pp. 18-20

Nielsen N., Ingvartsen L.K., 2000. Niacin for dairy cows. DJF Report Animal Husbandry No. 20.

Faculty of Agricultural Sciences, Aarhus Universitet (Denmark)

NNR, 2005. Nordic Nutrition Recommendations. Report 3. Nordiska Ministerådet, Copenhagen Nozière P., Graulet B., Lucas A., Martin B., Grolier P., Doreau M., 2006a. Carotenoids for ruminants:

From forages to dairy products. Anim. Feed Sci. Tech. 131, 418-450

Nozière P., Grolier P., Durand D., Ferlay A., Pradel P., Martin B., 2006b. Variations in carotenoids, fat-soluble micronutrients, and colour in cows plasma and milk following changes in forage and feeding level. J. Dairy Sci. 89, 2634-2648

NRC, 2001. Nutrient Requirements of Dairy Cattle. 7th revised Edition. National Academy Press, Washington, DC

O’Brian B., Mehra R., Connolly J.F., Harrington D., 1999. Seasonal variation in the composition of Irish manufacturing and retail milks. 4: Minerals and trace elements. Irish J. Agr. Food. Res. 38, 87-99

Ortman K., Pehrson B., 1999. Effect of selenate as a feed supplement to dairy cows in comparison to selenite and selenium yeast. J. Anim. Sci. 77, 3365-3370

Öste R., Jägerstad M., Andersson I., 1997. Vitamins in milk and milk products. In: P.F. Fox (Editor).

Advanced Dairy Chemistry, Chapter 3. Chapman & Hall, New York

Pennington J.A.T., 1990. Iodine concentrations in US milk: variation due to time, season and region.

J. Dairy Sci. 73, 3421-3427

Penniston K.L., Tanumihardjo S.A., 2006. The acute and chronic toxic effects of vitamin A. Amer.

J. Clin. Nutr. 83, 191-201

Péréz A., Lorenzo M., Cabrera C., Lopez C., 2002. Influence of enrichment with vitamins and minerals on the bioavailability of iron in cow’s milk. J. Dairy Res. 69, 473-481


Pfeffer E., Beede D.K., Valk H., 2005. Nitrogen and phosphorus nutrition of cattle. In: E. Pfeffer,

A. Hristov (Editors). Phosphorus Metabolism in Ruminants and Requirements of Cattle. CABI Publishing, pp. 195-237

Rasmussen M.D., Galton M.D., Pettersson L.G., 1991. Effects of premilking teat preparation on spores of anaerobes, bacteria and iodine residues in milk. J. Dairy Sci. 73, 3421-3427

Renner E., Schaafsma G., Scott K.J., 1989. Micronutrients in milk . In: E. Renner (Editor).

Micronutrients in Milk and Milk-Based Food Products. Elsevier Applied Science, London, pp. 1-70

RIKSMATEN, 1997-98. Dietary habits and nutrient intake in Sweden 1997-98. The second national food consumption survey (in Swedish). Information and Nutrition Department, Swedish National Food Administration, Uppsala (Sweden)

Saikat S.Q., Carter J.E., Mehra A., Smith B., Stewrt A., 2004. Goitre and environmental iodine deficiency in the UK-Derbyshire: A review. Environ. Geochem. Health 26, 395-401

Schwab E.C., Schwab C.G., Shaver R.D., Girard C.L., Putnam D.E., Whitehouse N.L., 2006.

Dietary forage and nonfiber carbohydrate contents influence B-vitamin intake, duodenal flow, and apparent ruminal synthesis in lactating dairy cows. J. Dairy Sci. 89, 174-187

Shaver R.D., Bal M.A., 2000. Effect of dietary thiamine supplementation on milk production by dairy cows. J. Dairy Sci. 83, 2335-2340

Spörndly R., 2003. Table of feeds for ruminants (in Swedish). Report No 257. Department of Animal Nutrition and Management, Swedish University of Agricultural Sciences, Uppsala (Sweden)

Swanson E.W., Miller J.K., Mueller F.J., Patton C.S., Bacon J.A., Ramsey N., 1990. Iodine in milk and meat of dairy cows fed different amounts of potassium iodide or ethylenediamine dihydro- iodide. J. Dairy Sci. 73, 398-405

Swedish Dairy Association, 1973. Composition of Dairy Milk in Sweden (1966-1971) (in Swedish).

Stockholm, Svenska Mejeriernas Riksförening

Swensson C., 2002. Ammonia release and nitrogen balances on South Swedish dairy farms 1997- 1999, Acta Univ. Agr. Sueciae, Agraria 333, SLU, Alnarp

Syrjäla-Qvist L., Aspila P., 1993. Selenium fertilization in Finland: effect on milk and beef production. Norwegian J. Agr. Sci., Suppl. 11, 159-167

Toledo P., Andren A., Björck L., 2002. Composition in raw milk from sustainable productions systems. Int. Dairy J. 12, 75-80

UK Ministry of Agriculture, 2000. Food Surveillance Information Sheet, Number 198, 2000 Iodine in Milk. http://archive.food.gov.uk/maff/archive/food/infsheet/2000/ no198/198milk. htm

Vaskonen T., 2003. Dietary minerals and modification of cardiovascular risk factors. J. Nutr.

Biochem. 14, 492-506

von Wowern F., 2006. Genetic factors and dietary salt intake as determinants of blood pressure and risk of primary hypertension. Dissertation. Lund University (Sweden)

Wakabayashi H., Yamauchi K., Takase M., 2006. Lactoferrin research, technology and applications.

Int. Dairy J. 16, 1241-1251

Weiss P., 2001. Effect of dietary vitamin C on concentrations of ascorbic acid in plasma and milk.

J. Dairy Sci. 84, 2302-2307

Weiss B., 2005. Sorting through the selenium question. Hoard’s Dairyman, September 25, 623 Witthöft C.M., Jägerstad M., 2003. Folates, nutritional significance. In: H. Roginski, J.W. Fuquay,

P.F. Fox (Editors). Encyclopaedia of Dairy Science. Academic Press, London, pp. 2714-2721

Journal of Animal and Feed Sciences, 16, Suppl. 1, 2007, 42–58


Effects of increasing the milk yield of dairy cows on milk composition


P. Huhtanen1,2 and M. Rinne


Animal Production Research, MTT Agrifood Research Finland FI-31600 Jokioinen, Finland


ABSTRACT


A meta-analysis of published and unpublished data (998 treatment means) comprising of milk production trials in dairy cows fed mainly grass silage-based diets was conducted to examine the effects of increasing milk yield on milk composition. The data was divided into seven subsets investigating the effects of level of concentrate, protein and fat supplementation, carbohydrate composition of the supplement, silage digestibility, silage fermentation quality or replacement of grass silages with legume silages. The relationships between milk yield and milk composition varied depending on dietary management. Both positive and negative relationships between milk yield and concentration of milk components (protein, fat and lactose) were observed. Correlation of milk fat and protein concentration ranged from negative to positive. Most of the relationships can be explained by relative changes in the supply of nutrients absorbed from the digestive tract.


KEY WORDS: protein, fat, lactose, feeding, nutrient supply, meta-analysis


INTRODUCTION


To optimize the economy of milk production the margin over feed cost within the limits of milk quota, animal health and environmental constraints should be maximized. In addition to milk volume, the income depends on milk composition (fat and protein concentration) and quality (bacteria, somatic cells). Milk pricing schemes are different between countries, but an increase in value of milk components - especially protein - at the expense of milk volume has been a general trend in most EU countries.


image

  1. Corresponding author: e-mail: pekka.huhtanen@mtt.fi

  2. Present address: Department of Animal Science, 269 Morrison Hall, Cornell University, NY 14853-4801, USA


    Depending on milk pricing schemes the value of the changes in milk yield and milk composition can differ widely, and therefore it would be important to know the effects of increased milk yield on milk composition. It is well established that both genetic and phenotypic correlations between milk yield and concentrations of fat and protein are negative. Genotypic regression coefficients in Finnish Ayrshire for milk protein and fat concentration on milk yield were

    -0.73 and -1.23 g/kg per kg increase in milk yield (Juga, 1992). The corresponding phenotypic regressions were -0.36 and -0.56, respectively. However, when milk yield is increased by improving the diet, the changes in milk composition may not follow the same pattern. For example, positive milk yield responses to higher concentrate supplementation (Gordon, 1984) or increased post-ruminal protein supply (Whitelaw et al., 1986) have been associated with increased protein concentration, whereas fat supplementation has often increased milk yield but decreased protein concentration (Wu and Huber, 1994; Lock and Shingfield, 2004). However, the current information about the changes in milk protein and fat concentration associated with increased milk yield is qualitative rather than quantitative. Both milk yield and milk composition are strongly influenced by stage of lactation, but this subject is not discussed in this paper.

    The objective of this study was to estimate the quantitative relationships between changes in milk yield and milk composition associated with increased nutrient supply. The analysis is based on a large data set from production trials in dairy cows fed diets based on grass silage.


    MATERIAL AND METHODS


    Description of the data set


    Mean treatment values were collected from dairy cow studies using ad libitum feeding of grass silage based diets (n=998). Approximately half of the experiments were conducted in UK, half in Finland and a few in Ireland and Sweden. For the Finnish experiments, also unpublished data was used.

    The data was divided into seven subsets based on the amount of concentrate (n=217), protein (n=363) and fat supplementation (n=29), carbohydrate composition of concentrate (n=114), silage digestibility (n=81) and fermentation quality (n=234), and replacement of grass silages with legume silages (n=48). Within each subset only the main factor varied; e.g., in studies investigating the effects of the concentrate level only the amount of concentrate varied but the composition of concentrate and forage were the same within a study. Number of treatment means, dry matter (DM) intake, dietary concentrations of crude protein (CP) and neutral detergent fibre (NDF), and milk production parameters for the whole data are shown in Table 1.


    Table 1. Feed intake and milk production



    Item


    n


    Mean

    Standard

    deviation


    Minimum


    Maximum

    DM intake, kg/d

    998

    17.9

    2.82

    9.9

    25.2

    In diet DM, g/kg

    CP

    998

    165

    21.5

    101

    252

    NDF

    998

    407

    50.0

    195

    571

    Milk production, kg/d

    milk

    998

    25.4

    5.05

    13.0

    45.8

    ECM

    998

    26.1

    5.14

    12.8

    42.1

    Milk composition, g/kg

    protein

    998

    32.1

    1.70

    25.9

    37.8

    fat

    998

    42.8

    3.96

    31.9

    55.0

    lactose

    985

    48.2

    1.66

    43.7

    52.3

    Component yield, g/d

    protein

    998

    814

    171

    359

    1449

    fat

    998

    1081

    217

    479

    1671

    lactose

    985

    1228

    250

    607

    2172


    Statistical analysis


    Mixed model regression procedure of SAS (Littell et al., 1996) was used to estimate linear and quadratic effects of independent response variables (e.g., amount of concentrate) on milk production parameters.

    The model was:


    0 1 ij 2 ij 0 1 ij ij

    Y = B + B X + B X2 + b + b X + e (1)


    2

    where B0 + B1Xij + B2X ij are the fixed effects, b0 and b1 are the random study effects (intercept and slope), i = 1…n studies and j = 1…ni values.

    In quadratic models only the linear effect of independent variable was a random factor, because the models using quadratic effect as a random factor did not generally converge. Mixed model analysis removes the variation in experimental protocols, animal types and laboratory assays which contribute to study effects in these regressions, i.e. the relationships between Y and X variables within a study are investigated. Rationale and further details of using mixed model analysis to integrate quantitative findings from multiple studies are described by St-Pierre (2001).

    The following parameters were used in the sub-datasets to estimate the responses in milk production parameters to changes in diet composition:


    1. Amount of concentrate (CDMI): concentrate DM intake

    2. Protein supplementation (PSuppl): CP concentration in the diet

    3. Fat supplementation (FAT): fatty acid concentration of the diet (fatty acids were estimated using empirical relationships between ether extract and fatty acids; unpublished)

    4. Carbohydrate composition of concentrate (CHO): NDF concentration in concentrate

    5. Silage digestibility (D-value): silage D-value

    6. Silage fermentation quality (SFQ): total acid concentration in the diet

    7. Replacement of grass with legume (Legume): proportion of legume in forage DM.


Adjusted Y values (adjusted observations) for milk production parameters were calculated as Y adjusted = Y predicted + residual. The Y predicted is simply value on the regression line (adjusted for random study effects). Residuals were generated by SAS OUTP option in the model.

The relationships between milk yield and milk composition were estimated by a simple regression model of the form:


Y = B0 + B1Xij + eij (2)

where B0 + B1Xij are the fixed effects.

2 ij

When the relationships appeared to be curvilinear also a quadratic term (B X2 )

was included in the model. It should be noted that adjusted values of milk yield and milk composition were used in this analyses.

A set point analysis was made for the relationships between milk yield and milk fat by Excel Solver. The data was fitted to linear regressions with a set point by minimizing the residual mean squared error between observed predicted values. The corresponding proportion of concentrate was estimated from the relationship from the quadratic regression equation between concentrate intake and milk yield.


RESULTS


The data showed large variation both in diet composition in terms of CP and NDF concentrations and in milk production (Table 1). Within sub-datasets the variation was smaller but still substantial.


Amount of concentrate


Milk yield, milk protein and lactose concentrations and yield of milk components increased quadratically with increased level of concentrate supplementation. Milk


fat concentration varied quadratically with the amount of concentrate reaching a maximum value at concentrate DM intake of 4.3 kg/d. Responses to increased concentrate feeding were relatively consistent within studies as indicated by small residual mean square error (RMSE) of adjusted milk yield (0.37 kg/d).

Higher milk yield resulting from increased concentrate feeding was positively associated with milk protein and lactose concentrations but negatively associated with milk fat concentration (Table 2). The effect of increased milk yield on fat concentration was curvilinear with relatively small changes below adjusted milk yield of 28 kg/d (Figure 1). Set point analysis described changes in


1

B1

s.e

P

2

2

Concentration, g/kg

protein 23.2 0.31

0.36

0.012

<0.001

0.807

0.38

fat 52.9 0.94

-0.38

0.036

<0.001

0.339

1.17

lactose 46.3 0.15

0.07

0.006

<0.001

0.424

0.19

Protein/fat 0.358 0.0182

0.015

0.0007

<0.001

0.690

0.023

Yield, g/d

protein -217 7.7

40.7

0.298

<0.001

0.989

9.6

fat 239 30.5

33.2

1.177

<0.001

0.787

37.9

lactose -58 6.6

50.5

0.254

<0.001

0.995

8.2

1 standard error

2 RMSE - residual mean squared error

Table 2. Effects of increased milk yield in response to increased concentrate feeding on milk composition and yield of milk components

image

Item B0 s.e.

Adj. R

RMSE


image


image


image


image


image


image


image


image


image


image

image

image

image

image

image

image

Fat in concentrate, g/kg

Figure 1. The effects of milk yield associated with increased amount of concentrate feeding on milk fat concentration


milk fat concentration much better than the linear trend (R2=0.60 vs 0.34). The set point was at adjusted milk yield of 28 kg/d, which coincides with a concentrate proportion of 0.57 in diet DM. Protein and fat concentrations were negatively correlated (r=-0.44; P<0.001).

The yield of milk components increased as milk yield increased with concentrate feeding (Table 2). The effects were very consistent for protein and lactose yields, but fat yield responses associated with increased milk yield were more variable. The slope of regression represents concentrations of protein, fat and lactose in incremental milk yield. For example, additional milk contained 40.7 and 33.2 g/kg of protein and fat, respectively.


Protein supplementation


Milk yield increased quadratically in studies investigating the effects of protein supplementation. The RMSE of adjusted milk yield was 0.47 kg/d. Milk yield was positively related to milk protein concentration and negatively to fat and lactose concentrations in these studies (Table 3). However, protein


Table 3. Effects of increased milk yield in response to protein supplementation on milk composition and yield of milk components

Item

B0

1

B1

s.e.

P

2

2

Concentration, g/kg

protein

25.1

0.32

0.27

0.012

<0.001

0.584

0.31

fat

58.0

0.90

-0.57

0.034

<0.001

0.437

0.87

lactose

50.5

0.20

-0.09

0.007

<0.001

0.307

0.19

milk urea, mg/L

-942

38.2

47.0

1.46

<0.001

0.797

28.6

corrected protein

28.7

0.41

0.11

0.016

<0.001

0.159

0.31

Protein/fat

0.316

0.0170

0.017

0.0006

<0.001

0.646

0.017

Yield, g/d

protein

-167

8.4

39.1

0.318

<0.001

0.977

8.2

fat

317

22.5

30.8

0.851

<0.001

0.783

21.9

lactose

40

6.0

45.6

0.226

<0.001

0.991

5.8

s.e.

Adj. R

RMSE

image


  1. standard error

  2. RMSE - residual mean squared error


supplementation increased significantly milk urea concentration with the mean response being 47 mg urea/kg additional milk. Consequently, the effect of increased milk yield on urea-corrected protein concentration was less than half of that observed for uncorrected protein concentration. Increased milk yield in response to supplementary protein feeding was associated with higher protein to fat ratio in milk. Additional milk contained 39.1, 30.8 and 45.6 g/kg of protein, fat and lactose, respectively. Milk protein or urea-corrected protein and fat concentration were negatively correlated (P<0.001).


image


image


image


image

image

image

image

image

image

image

Figure 2. Relationship between milk urea and lactose concentrations in protein supplementation studies (n=265 diets)


Milk urea concentration was negatively related to lactose concentration (Figure 2). Although the variation in adjusted lactose concentration was small (range from

47.4 to 48.7 g/kg), the effect of urea concentration on lactose concentration was strongly significant (P<0.001).


Fat supplementation


Milk yield increased quadratically with increasing fatty acid concentration of diet reaching maximum at 48 g/kg DM in fat supplementation studies. Milk protein concentration decreased (P<0.001) with increasing milk yield, but fat and lactose concentrations were not associated with milk yield (Table 4). The yields of milk components increased with milk yield, but the slope of regression was only

16.1 for milk protein yield.


Table 4. Effects of increased milk yield in response to fat supplementation on milk composition and yield of milk components

image

1

B1

s.e.

P

2

2

Concentration, g/kg

protein 47.0 2.43

-0.59

0.092

<0.001

0.585

0.44

fat 43.0 8.41

-0.16

0.319

0.63

-0.028

1.52

lactose 45.3 2.75

0.06

0.104

0.54

-0.023

0.50

protein/fat 1.129 0.1802

-0.012

0.0068

0.09

0.068

0.033

Yield, g/d

protein 407 59.8

16.1

2.268

<0.001

0.637

10.8

fat 72 233.6

35.5

8.869

<0.001

0.349

42.3

lactose -69 76.2

49.6

2.892

<0.001

0.913

13.8

1 standard error

2 RMSE - residual mean squared error

Item B0 s.e.

Adj. R

RMSE


Carbohydrate composition of the energy supplement


Carbohydrate composition of the concentrate had only minor effects on milk yield as indicated by the narrow range (24.9-26.8 kg/d) and the small coefficient of variation (1.24%) in adjusted milk yield, i.e. within a study the differences between diets were very small.

Milk protein concentration decreased (P<0.001) and lactose concentration increased (P<0.01) with increased milk yield (Table 5), whereas milk fat


Item

B0

1

B1

s.e.

P

2

2

Concentration, g/kg

protein

49.0

3.37

-0.66

0.131

<0.001

0.175

0.45

fat

37.2

3.63

0.16

0.141

0.27

0.002

0.48

lactose

43.2

1.47

0.16

0.057

0.006

0.062

0.18

Protein/fat

1.263

0.0965

-0.019

0.0038

<0.001

0.177

0.013

Yield, g/d

protein

310

84.2

19.9

3.279

<0.001

0.241

11.1

fat

-134

181.7

46.5

7.076

<0.001

0.272

24.0

lactose

-27

40.2

48.3

1.565

<0.001

0.903

4.8

Table 5. Effects of changes in milk yield associated with concentrate carbohydrate composition on milk composition and yield of milk components´

s.e.

Adj. R

RMSE

image


  1. standard error

  2. RMSE - residual mean squared error


concentration was not significantly influenced by milk yield in concentrate carbohydrate composition studies. Protein to fat ratio in milk was negatively related to milk yield. The correlation between milk fat and protein concentrations was small and insignificant. Milk component yields increased with milk yield, but the slope for protein yield was markedly lower than the mean protein concentration in these studies (19.9 vs 32.1 g/kg), i.e. extra milk produced in response to changing concentrate carbohydrate composition had a low protein concentration.


Silage digestibility


Milk yield increased linearly in studies investigating the effects of silage digestibility on milk production. Milk yield was positively correlated with all milk components, although numerically the increase in lactose was small (Table 6). Due to greater increase in milk protein compared with fat concentration, the protein to fat ratio in milk increased with increased yield. When silage digestibility was improved by harvesting at earlier stage of grass growth additional milk had both high protein and fat concentrations as indicated by high slopes of protein and fat


yield on milk yield (39.4 and 50.4 g/d, respectively). Protein and fat concentrations were not significantly correlated (r=0.14; P=0.11).


Item

B0

1

B1

s.e.

P

2

2

Concentration, g/kg

protein

22.4

1.59

0.41

0.065

<0.001

0.323

0.79

fat

37.8

2.30

0.19

0.094

0.047

0.037

1.15

lactose

46.6

0.51

0.05

0.021

0.013

0.064

0.26

Protein/fat

0.609

0.0534

0.006

0.0022

0.005

0.084

0.027

Yield, g/d

protein

-173

30.2

39.4

1.23

<0.001

0.927

15.1

fat

-192

44.9

50.4

1.84

<0.001

0.904

22.5

lactose

13

15.3

47.4

0.63

<0.001

0.986

7.7

Table 6. The effects of increased milk yield in response to improved silage digestibility on milk composition and yield of milk components

s.e.

Adj. R

RMSE

image


  1. standard error

  2. RMSE - residual mean squared error


Silage fermentation quality


Milk and especially fat and protein yields decreased linearly with increasing total acid concentration in silage. In-silo fermentation was manipulated by using different additive treatments (e.g., untreated, inoculants, enzymes, acids). Milk fat and protein concentrations were positively (P<0.001) related to milk yield in studies investigating the effects of silage fermentation characteristics (Table 7).


1

B1

s.e.

P

2

2

Concentration, g/kg

protein 21.8 1.42

0.43

0.059

<0.001

0.185

0.61

fat 22.4 3.10

0.89

0.129

<0.001

0.167

1.34

lactose 51.6 0.76

-0.10

0.032

0.003

0.035

0.33

Protein/fat 0.858 0.0394

-0.005

0.0016

0.002

0.037

0.017

Yield, g/d

protein -180 33.8

39.5

1.41

<0.001

0.771

14.6

fat -485 79.1

63.6

3.30

<0.001

0.615

34.2

lactose 78 19.1

46.0

0.80

<0.001

0.935

8.3

1 standard error

2 RMSE - residual mean squared error

Table 7. The effects of milk yield on milk composition and yield of milk components in studies investigating the effects of silage fermentation quality

image

Item B0 s.e.

Adj. R

RMSE


In silage fermentation studies milk yield and lactose concentration were negatively correlated. Protein to fat ratio in milk was negatively (P<0.01) related to milk yield. Incremental milk yield had high protein, and especially fat concentration. In silage fermentation studies milk fat and protein concentrations were strongly and positively correlated (r=0.72; P<0.001).


Replacement of grass with legume silages


Diets containing white clover silages were excluded from the analysis, because of very low NDF concentrations and generally different milk yield and composition responses compared with red clover, the most commonly used forage legume in Northern Europe. Milk protein concentration decreased with increased milk yield in studies examining the replacement of grass silages with legume silages (Table 8). Also milk fat concentration was negatively associated


Item

B0

1

B1

s.e.

P

2

2

Concentration, g/kg

protein

37.0

1.65

-0.20

0.059

0.001

0.186

0.39

fat

48.0

5.38

-0.18

0.193

0.35

-0.002

1.27

lactose

44.6

1.14

0.13

0.041

0.003

0.159

0.27

Protein/fat

0.774

0.0903

-0.0016

0.00324

0.62

-0.016

0.021

Yield, g/d

protein

173

45.8

25.1

1.64

<0.001

0.831

10.8

fat

244

146.6

34.1

5.26

<0.001

0.466

34.5

lactose

-101

48.1

51.8

1.73

<0.001

0.950

11.3

Table 8. The effects milk yield on milk composition and yield of milk components in studies investigating the effects of replacement of grass silage with legume silages

s.e.

Adj. R

RMSE

image


  1. standard error

  2. RMSE - residual mean squared error


with milk yield, but the effect was not significant. Lactose concentration increased with milk yield (P<0.01). Due to reduced concentrations of protein and fat in milk, additional milk had relatively low concentrations of protein and fat.


DISCUSSION


The objective of the present study was to examine quantitative relationships between milk yield and milk composition, when the most common dietary means to increase milk yield were investigated. A mixed model regression analysis was


used to exclude study effects from the total variation, i.e. relationships between adjusted values within a study were investigated.


Milk protein concentration


Protein is the most valuable milk component and therefore there has been a continuous interest to increase milk protein concentration by nutritional means. The present analysis demonstrated that in most cases when the nutrition of cows is improved (CDMI, PSuppl, D-value and SFQ studies), milk yield and protein concentrations were positively correlated. The positive effects of the level of concentrate supplementation on both milk yield and protein concentration are well established, but in many protein supplementation studies the effects have failed to reach statistical significance. The effect of concentrate level on protein concentration is quadratic, and at high levels of supplementation milk protein concentration can decline (e.g., Ferris et al., 1999). Significant positive effects of both improved silage digestibility (Rinne, 2000) and restricted in-silo fermentation (Huhtanen et al., 2003) on milk protein concentration have been reported from meta-analyses. In both cases these responses can be attributed to increased silage DM intake, and consequently increased energy supply to rumen microbes. Restricting in-silo fermentation will also increase microbial protein supply (Harrison et al., 2003), because water solubles carbohydrates provide more energy for the growth of rumen microbes than silage fermentation products.

A general feature of the four nutritional means is that both the supply of metabolizable energy and protein (amino acids absorbed from small intestine; AAT) calculated according to MTT (2006) increased. However, there were substantial differences in the relative changes in ME and AAT supply (Table 9).


image

Table 9. The effects of response variables on metabolizable energy (ME) and protein (AAT) intake and the ratio of protein to lactose (PY/LY) in additional milk yield



Subject


Variable

Intake response ME AAT

MJ/d g/d


AAT/ME

g/MJ


PY/LY

CDMI1

CDMI, g/kg diet DM

7.51

72.2

9.61

0.80

PSuppl2

g CP3/kg diet DM

0.222

5.64

25.37

0.85

D-value

g DOM4/kg silage DM

0.325

2.56

7.87

0.81

SFQ5

g TA6/kg diet DM

-0.333

-2.55

7.68

0.77

1 concentrate dry matter intake; 2 protein supplementation; 3 crude protein; 4 digestible organic matter;

5 silage fermentation quality; 6 total acids


Despite a wide range in the additional substrate supply the regression coefficients of protein yield on lactose yield were similar for the four means of dietary manipulation. This suggests that it is very difficult to increase milk protein yield


more than lactose yield by dietary treatments. With post-ruminal casein infusion, which probably results in the highest amino acid to energy ratio in incremental nutrient supply (approximately 50 g AAT per MJ ME), the protein to fat ratio in additional milk yield was slightly above 1.0 (Huhtanen, 1998). Marginal lactose yield response to increased ME supply was markedly higher in PSuppl studies

(7.1 g per MJ ME) compared with CDMI (4.9), D-value (4.6) and SFQ (4.0) studies, respectively. This indicates that part of the increased supply of AAT from supplementary protein was used for gluconeogenesis and therefore was not completely available for milk protein synthesis. Indeed, abomasal infusion of casein has shown to increase glucose flux in dairy cows (Clark et al., 1977).

In PSuppl studies a large proportion of increased milk protein concentration resulted from increased milk urea concentration. This conclusion is based on an assumption that milk analysers were calibrated for crude protein, which was the case at least in the Finnish studies. In some studies milk protein was analysed by Kjeldahl method. It should also be noted that increases in milk yield in PSuppl studies were associated with large increases in milk urea concentration, which is a strong indicator of reduced efficiency of N utilization (Nousiainen et al., 2004).

Fat supplementation often increased milk yield but decreases milk protein concentration (e.g., Wu and Huber, 1994; Lock and Shingfield, 2004), in agreement with the present study. Fat supplements have often been used to replace starchy supplements, which reduces the concentration of metabolizable protein in the diet. However, increasing amino acid supply by post-ruminal casein infusion did not alleviate the adverse effect of fat supplementation on milk protein concentration (Cant et al., 1993).

In the present meta-analysis milk yield and protein concentration were negatively correlated in studies investigating the substitution of cereal grains by fibrous by-products. In single studies published in the literature the effects have been variable. The adverse effect on milk protein concentration sometimes reported for fibrous by-products may be related to the inclusion of fat supplements in order to compensate for the lower energy concentration of fibrous by-products compared with cereal grains. In the present data, the concentrate fat and NDF concentrations were positively correlated (P<0.001) suggesting that increased diet fat concentration may, at least partly, explain the lower milk protein concentration with increasing concentrate NDF concentration. When low-fat high NDF by- products such as sugar-beet pulp were compared with barley, no differences in milk protein concentration were observed (Castle et al., 1981; Huhtanen, 1987). It should also be noted that the effects of concentrate carbohydrate composition on milk production were marginal and therefore the overall effect on milk protein concentration is not very large despite strongly negative regression coefficient.

The negative relationship between milk yield and protein concentration, when grass silage was partly or completely replaced with legume, mainly red-clover


silages, is difficult to explain. Replacing grass silage with legumes increased milk yield quadratically reaching the maximum when legumes comprised proportionally

0.72 of the total silage DM. Protein flow to the small intestine has increased when red-clover has replaced grass silage in the diet (Dewhurst et al., 2003; Vanhatalo et al., 2006) but increased protein flow has been utilized inefficiently in milk protein synthesis. Protein to lactose ratio in incremental milk yield was 0.47 in legume studies, which is much lower than those shown in Table 9 but slightly higher than in FAT (0.34) and CHO studies (0.31). This suggests that the nutrient supply from diets based on red-clover silages favoured lactose rather than protein yield. The low ratio between protein and lactose yield increases is similar to that observed in post-ruminal glucose infusion studies (Huhtanen, 1998). However, rumen fermentation pattern and protein flow measurements do not suggest greater relative increases in glucogenic nutrients compared with aminogenic nutrients in legume studies (Dewhurst et al., 2003; Vanhatalo et al., 2006).


Milk fat concentration


In most cases increases in milk yield were associated with reduced milk fat concentration. When the amount of concentrates was increased, milk fat concentration was not markedly influenced before adjusted milk yield reached 28 kg/d corresponding proportionally 0.57 concentrate DM of total DM. A similar set point pattern was observed for milk fat yield; additional kg of milk increased fat yield by 40.9 g when the proportion of concentrate was below 0.57, but above it milk fat yield decreased by 60 g per kg increase in milk yield. Set point analysis explained the variation between milk and fat yield better than linear regression (R2 0.90 vs 0.79). The study of Gordon (1984) is a good example that in cows fed grass silage milk fat concentration is resistant to changes in the level of concentrate supplementation. The small responses in milk fat concentration to increased concentrate feeding are consistent with small effects of dietary starch concentration and proportion of concentrate on rumen VFA pattern in cows fed grass silage-based diets (Sveinbjörnsson et al., 2006). Weiss et al. (2003) concluded that a feature of diets based on grass silage is that the profile of the three major ruminal VFA are resistant to changes in response to addition of starchy concentrates. At high levels of concentrate inclusion, the decreases in both milk fat concentration and yield may be related to changes in rumen biohydrogenation and increased flow of trans-10 isomers of C18:1 to the small intestine (Griinari et al., 1998).

The negative relationship between milk yield and milk fat concentration in studies investigating the effects of increased protein supplementation is more likely to be a dilution effect rather than a consequence of changes in the supply of milk fat precursors to the mammary gland. A strong positive relationship between adjusted milk and fat yield supports this suggestion. Protein supplementation


of grass silage-based diets increases both silage DM intake (Oldham, 1984; Huhtanen, 1998) and diet digestibility (Oldham, 1984) providing precursors for increased milk fat synthesis.

Increased milk yield in response to improved silage digestibility was associated with a small increase in milk fat concentration in spite of reduced NDF concentration in the diet. This can be related to rumen fermentation pattern high in butyrate in cows fed highly digestible silages (Rinne et al., 2002). Intraruminal butyrate infusions have increased milk fat concentration (Miettinen and Huhtanen, 1996).

Increased milk yield resulting from restricted silage fermentation was associated with increased fat concentration as indicated by a high (63.6 g/kg) fat concentration in the additional milk yield. These responses are likely to be explained by increased silage DM intake (Huhtanen et al., 2003) with reduced total acid concentration and associated changes in rumen fermentation pattern. Residual sugars in restrictively fermented silages will favour increased proportions of acetate and butyrate in rumen VFA (van Vuuren et al., 1995; Harrison et al., 2003), whereas lactic acid is fermented to propionate (van Vuuren et al., 1995; Sveinbjörnsson et al., 2006). The strong positive correlation between fat and protein concentrations in silage fermentation studies is likely to be explained by relative changes in milk fat precursors; the supply of both fat (acetate and butyrate) and protein precursors (microbial protein) increase, whereas the supply of main lactose precursor (propionate) decreases as the extent of in-silo fermentation is restricted.


Milk lactose concentration


Lactose is the main regulator of osmotic pressure in milk and lactose synthesis determines the milk volume. Generally the effects of diet composition on lactose concentration have been small and seldom statistically significant. Fish meal supplementation (Broderick, 1992) and increased butyrate supply manipulated by intraruminal infusions (Miettinen and Huhtanen, 1996) are few examples of studies, in which significant dietary effects on lactose concentration have been reported.

Although in single studies dietary effects on lactose concentration are seldom significant, the present meta-analysis showed strongly significant relationships between response variables (e.g., concentrate DM intake, dietary CP concentration) and lactose concentration, and between milk yield and lactose concentration. Regression coefficients between milk yield and lactose concentration varied from approximately 0.15 g/kg per kg milk in CDMI, CHO and Legume studies to approximately -0.10 in PSuppl and SFQ studies. At least in CDMI, PSuppl and SFQ studies there is enough data (>200 treatment means) allowing to hypothesize possible mechanisms.


In CDMI studies glucose supply increases with increased concentrate supplementation mainly due to increased DM intake and increased duodenal starch flow, but possibly also because of changes in rumen fermentation pattern, at least at high proportions of concentrate. Entry rate of glucose is closely related to digestible energy intake (Elliot, 1980) and increases approximately 115 g per kg increase in DM intake. In the present data milk yield increased 1.3 kg per kg increase in total DM intake, when the amount of concentrate supplementation was increased. This corresponds to about 90 g increase in glucose requirement (Danfær, 1994), i.e. the supply of glucose increased more than the requirement with high concentrate diets.

The negative relationship between milk yield and lactose concentration in protein supplementation studies was associated with increased milk urea concentration. It is possible that urea increased the osmotic pressure in milk and therefore less lactose was needed to excrete additional milk produced with improved amino acid supply. A similar negative relationship between urea and lactose concentrations was observed in practical milk samples (Nousiainen J., personal communication). However, although the negative relationship between milk yield and lactose concentration was highly significant, lactose concentration in additional milk was only marginally lower than the mean lactose concentration

(45.6 vs 48.0) in protein supplementation studies.

Milk lactose concentration increased significantly with total acid concentration in the diet. Because increased TA concentration was associated with reduced milk yield, lactose concentration decreased with milk yield when silage fermentation was restricted. As discussed above, molar proportion of propionate in ruminal VFA is directly related to the concentration of lactic acid in silage. High lactate silages have sometimes increased plasma glucose concentration compared with restrictively fermented silages (Heikkilä et al., 1998; Shingfield et al., 2002) suggesting that glucose supply may limit milk yield in cows fed restrictively fermented silages.


CONCLUSIONS


The present analysis demonstrated that when milk yield is manipulated by dietary management, the relationships between milk yield and milk composition are in most cases different from genotypic and phenotypic correlations. Milk protein concentration increases with milk yield, when the nutrition of cows is improved by feeding more concentrates and supplementary protein or when the digestibility or fermentation quality of silage is improved. Milk fat concentration is reduced with increased concentrate and protein supplementation, but the effects on concentrate feeding on fat concentration are small below the set point in concentrate proportion (0.57 of total DM). The relationships between milk fat


and protein concentration were variable depending on how diet composition was changed ranging from negative (e.g., CDMI) and non-significant (e.g., silage D-value) to strongly positive (silage fermentation quality). Statistically significant positive relationships between milk yield and lactose concentration were observed. Generally the observed relationships can be explained by relative changes in the supply of glucogenic, lipogenic and aminogenic nutrients absorbed from the digestive tract.


REFERENCES


Broderick G.A., 1992. Relative value of fish meal versus solvent soybean meal for lactating dairy cows fed alfalfa silage as sole forage. J. Dairy Sci. 75, 174-183

Cant J.P., DePeters E.J., Baldwin R.L., 1993. Mammary amino acid utilisation in dairy cows fed fat and its relationship to milk protein depression. J. Dairy Sci. 76, 762-774

Castle M.E., Gill M.S., Watson J.N., 1981. Silage and milk production: a comparison between barley and dried sugar-beet pulp as silage supplements. Grass Forage Sci. 36, 319-324

Clark J.H., Spires H.R., Derrig R.G., Bennink M.R., 1977. Milk production, nitrogen utilization and glucose synthesis in cows infused postruminally with sodium caseinate and glucose. J. Nutr. 107, 631-644

Danfær A., 1994. Nutrient metabolism and utilization in the liver. Livest. Prod. Sci. 39, 115-127 Dewhurst R.J., Evans R.T., Scollan N.D., Moorby J.M., Merry R.J., Wilkins R.J., 2003. Comparisons

of grass and legume silages for milk production. 2. In vivo and in sacco evaluations of rumen function. J. Dairy Sci. 86, 2612-2621

Elliot J.M., 1980. Propionate metabolism and vitamin B12. In: Y. Ruckebush, P. Thivend (Editors).

Digestive Physiology and Metabolism in Ruminants. MTP Press, Lancaster (England), pp. 485

Ferris C.P., Gordon F.J., Patterson D.C., Kilpatrick D.J., Mayne C.S., McCoy M.A., 1999. The response of dairy cows of high genetic merit to increasing proportion of concentrate in the diet with a high and medium feed value silage. J. Agr. Sci. 136, 319-329

Gordon F.J., 1984. The effect of level of concentrate supplementation given with grass silage during the winter on the total lactation performance of autumn-calving dairy cows. J. Agr. Sci. 102, 163-179

Griinari J.M., Dwyer D.A., McGuire M.A., Bauman D.E., Palmquist D.L., Nurmela K.V.V., 1998.

Trans-octadecenoic acids and milk fat depression in lactating dairy cows. J. Dairy Sci. 81, 1251- 1261

Harrison J., Huhtanen P., Collins M., 2003. Perennial grasses. In: D.R. Buxton, R.E. Muck, J.H. Harrison (Editors). Silage Science and Technology. American Society of Agronomy, pp. 665- 747

Heikkilä T., Toivonen V., Huhtanen P., 1998. Effects of and interactions between the extent of silage fermentation and protein supplementation in lactating dairy cows. Agr. Food Sci. Finland 7, 329-343

Huhtanen P., 1987. The effect of dietary inclusion of barley, unmolassed sugar beet pulp and molasses on milk production, digestibility and digesta passage in dairy cows given silage based diet. J. Agr. Sci. Finland 59, 101-120

Huhtanen P., 1998. Supply of nutrients and productive responses in dairy cows given diets based on restrictively fermented silage. Agr. Food Sci. Finland 7, 219-250


Huhtanen P., Nousiainen J.I., Khalili H., Jaakkola S., Heikkilä T., 2003. Relationships between silage fermentation characteristics and milk production parameters: analyses of literature data. Livest. Prod. Sci. 81, 57-73

Juga J., 1992. Estimation of variances and covariances of milk traits by REMP with individual animal model. Acta Agr. Scand., Sect. A, Anim. Sci. 42, 198-204

Littel R.C., Milliken G.A., Stroup W.W., Wolfinger R.D., 1996. SAS® System for Mixed Models.

SAS Inst. Inc., Cary, NC

Lock A.L., Shingfield K.J., 2004. Optimising milk composition. In: E. Kebreab, J. Mills, D.E. Beever (Editors). Dairying-Using Science to Meet Consumers’ Needs. British Society of Animal Science, Publication No. 29, Nottingham University Press, Loughborough (UK), pp. 107-188

Miettinen H., Huhtanen P., 1996. The effects of ruminal propionate to butyrate ratio on milk production and blood metabolites in dairy cows fed a grass silage based diet. J. Dairy Sci. 79, 851-861

MTT, 2006. Feed Tables and Feeding Recommendations (in Finnish). Jokioinen: MTT Agrifood Research Finland. Updated 14 February 2006. Cited 16 June 2006. Available on the Internet: http://www.agronet.fi/rehutaulukot/. URN:NBN:fi-fe20041449

Nousiainen J., Shingfield K., Huhtanen P., 2004. Evaluation of milk urea nitrogen as a diagnostic of protein feeding. J. Dairy Sci. 87, 386-398

Oldham J.D., 1984. Protein energy relationships in dairy cows. J. Dairy Sci. 67, 1090-1114

Rinne M., 2000. Influence of the timing of the harvest of primary grass growth on herbage quality and subsequent digestion and performance in the ruminant animal. Academic Dissertation, University of Helsinki, Department of Animal Science, Publications 54, pp. 42 + 5 encl., Available on the Internet: http://ethesis.helsinki.fi/julkaisut/maa/kotie/vk/rinne/

Rinne M., Huhtanen P., Jaakkola S., 2002. Digestive processes of dairy cows fed silages harvested at four stages of maturity. J. Anim. Sci. 80, 1986-1998

Shingfield K., Jaakkola S., Huhtanen P., 2002. Effect of forage conservation method, concentrate level and propylene glycol on diet digestibility, rumen fermentation, blood metabolite concentrations and nutrient utilization of dairy cows. Anim. Feed Sci. Tech. 97, 1-21

St-Pierre N.R., 2001. Integrating quantitative findings from multiple studies using mixed model methodology. J. Dairy Sci. 84, 741-755

Sveinbjörnsson J., Huhtanen P., Udén P., 2006. The Nordic dairy cow model, Karoline - Development of volatile fatty acid sub-model. In: E. Kebreab, J. Dijkstra, A. Bannink, W.J.J. Gerrits, J. France (Editors). Nutrient Digestion and Utilization in Farm Animals: Modelling Approaches. CAB International, pp. 1-14

Vanhatalo A., Kuoppala K., Ahvenjärvi S., Rinne M., 2006. The effect of red clover silage on the nutrient supply to dairy cows (in Finnish). Maataloustieteen Päivät 2006 (electronic publication). Suomen Maataloustieteellisen Seuran julkaisuja No 21. A. Hopponen (Editor). Available on the Internet: http://www.smts.fi/pos06/1105.pdf. ISBN 951-9041-49-4

van Vuuren A.M., Huhtanen P., Dulphy J.-P., 1995. Improving the feeding and health value of ensiled forages. In: M. Journet, E. Grenet, M.-H. Farce, M. Theriez, C. Demarquilly (Editors). Recent Developments in the Nutrition of Herbivores. INRA, Paris, pp. 297-307

Weiss W.P., Chamberlain D.G., Hunt C.W., 2003. Feeding silages. In: D.R. Buxton, R.E. Muck

J.H. Harrison (Editors). Silage Science and Technology. American Society of Agronomy, pp. 665-747

Whitelaw F.G., Milne J.S., Ørskov E.R., Smith J.S., 1986. The nitrogen and energy metabolism of lactating cows given abomasal infusion of casein. Brit. J. Nutr. 55, 537-556

Wu Z., Huber J.T., 1994. Relationship between dietary-fat supplementation and milk protein- concentration in lactating cows - a review. Livest. Prod. Sci. 39, 141-155

Journal of Animal and Feed Sciences, 16, Suppl. 1, 2007, 59–64


Fatty acids and flavours in milk from dairy cows fed no synthetic vitamins*


H. Danielsson1,4, B. Johansson1, E. Nadeau1, K. Persson Waller2 and S.K. Jensen3


1Department of Animal Environment and Health, Swedish University of Agricultural Sciences

P.O. Box 234, SE-532 23 Skara, Sweden

2Department of Pigs, Poultry and Ruminants, National Veterinary Institute (SVA) SE-751 89 Uppsala, Sweden

3Department of Animal Health, Welfare and Nutrition, Danish Institute of Agricultural Sciences, Research Centre Foulum

P.O. Box 50, DK-8830 Tjele, Denmark


ABSTRACT


The aim of this study was to investigate the effects of feeding no synthetic vitamins to dairy cows, fed a 100% organic diet, on the organoleptic quality and fatty acid composition of the milk. A 12-month study was performed at Tingvall Organic Dairy Research Farm. Individual milk samples for organoleptic analysis were collected at six occasions from 50 cows, equally allocated into two treatments, one with vitamin supplementation and one without. Monthly composited milk samples from each treatment were collected for analysis of organoleptic quality and fatty acid composition. The results indicate that supplementation of synthetic vitamins according to Swedish recommendations do not generally affect organoleptic quality and fatty acid composition of the milk.


KEY WORDS: off-flavour, antioxidant, fatty acid, milk quality


INTRODUCTION


Oxidation of polyunsaturated fatty acids (PUFA) causes oxidative off-flavours in milk. Both ß-carotene and α-tocopherol are important antioxidants and, consequently, limit oxidation of fatty acids (FA; Charmley and Nicholson, 1994; Jensen et al., 1999). Results by Ellis et al. (2006) have shown that organic milk has a higher content of PUFA and n-3 FA than milk from conventional herds. Both


image

3 Corresponding author: e-mail: Kerstin.svennersten@huv.slu.se


2001). Plasmin causes degradation of β-casein to γ-casein and proteose-peptone, which influence the quality of milk for cheese production (Bastian, 1996).

The mechanism behind these effects is not fully evaluated. Both technical and biological reasons have been proposed to explain the affects on milk fat. Increased air exposure during milking which can damage the fat globules could be one reason. Raised enzymatic activity of fatty acid synthetase and acetyl CoA carboxylase, responsible for the de novo synthesis of milk fat, and thereby a higher proportion of short-chained fatty acids in the milk, is another suggestion (Klei et al., 1997). The nutritional status, along with MF, can influences milk FFA content (Svennersten- Sjaunja et al., 2002). For protein, increased MF shortens the time in which milk is stored in the udder, whereby proteolytic enzymes such as plasmin, have less time to degrade the milk proteins (Sorensson et al., 2001). Lower plasmin activity due to increased MF could be a result of improved integrity of the tight junctions between the milk secreting cells in the udder because of less udder pressure.

The aim of the present study was to evaluate the effects of increased MF when the effects of environment and nutrition were eliminated and mainly udder related effects on milk synthesis were considered. The hypothesis was that there is no difference between udder halves (UH) when they are milked with the same frequency but when MF is increased in one UH both yield and composition will be affected in that specific UH. The present report is a summary of Wiking et al. (2006) and Svennersten-Sjaunja et al. (2006).


MATERIAL AND METHODS


The study was carried out at Kungsängens Research Centre, Swedish University of Agricultural Sciences (Uppsala). Eleven cows of the Swedish Red breed in lactation number 1-4 and lactation week 8-50 participated in the study. The average milk somatic cell count (SCC) before the initiation of the experiment was below 100 000 cells/mL milk in the cow composite milk. Quarter strip milk samples were analysed for SCC during the experiment.

The study lasted for 12 days with two five-day long periods. In the first period, the cows were milked on each UH twice daily at 12-h intervals; in the second period they were milked twice daily on one UH and four times daily at 6-h intervals on the contralateral UH.

Milk yield was registered at every milking. Milk samples were taken from both UH. FFA was analysed in both fresh milk and milk cold stored for 24 h. The other milk samples were analysed in fresh milk only. Samples were analysed for content of fat, protein and lactose by Mid Infrared photospectroscopy (MilkoScan FT120 FOSS Electric, Denmark). For analysis of FFA, fatty acid composition, fat globule size and activity of γ-glutamyl transpeptidase (see Wiking et al.,


2006). Casein content was determined by the rennet method (Arla Food analytical directions 30:004, 001210), plasmin, plasminogen-derived activity and degree of proteolysis were determined as described by Wiking et al. (2002) and Larsen et al. (2004). Content of Na and K ions was determined by flame photometry (Flame Photometer FF-IL 943, Instrumentation Laboratory Milan, Italy) and SCC was analysed by electronic fluorescence based cell counting (Fossomatic 5000, Foss Electric, Denmark). Paired t-test was used to evaluate effects of increased unilateral milking frequency.


RESULTS AND DISCUSSION


The SCC in the quarter strip milk yield was 116 000 cells/mL (range 11 000- 569 000) on average. The udder health was judged as good since SCC is higher in strip milk compared to SCC in composite milk samples (Östensson et al., 1988). No differences between the two UH in milk yield and composition were observed in period one verifying that the proposed hypothesis could be used.

The milk yield was 4.5% higher in the more frequently UH. No or only minor difference between the UH in period two were observed for the content of milk fat, protein and lactose (Table 1).


Table 1. Milk yield (kg), fat, protein and lactose content (%) in udder halves (UH) milked twice daily in period one and one UH was milked twice daily while the contralateral was milked four times in period two. Results are expressed as mean and standard deviation (SD); n=11

image

Period 1 Period 2

(control period)

1

(experimental period)

milking frequency Diff

milking frequency Diff

2 x 2 x 2 x 4 x

Milk yield

14.32 (4.45)

14.20 (3.95)

0.11 (0.84)

14.77 (5.26)

15.42 (4.76)

-0.65 (1.43)*2

Fat

4.56 (0.67)

4.57 (0.58)

-0.01(0.17)

4.71 (0.70)

4.59 (0.68)

0.12 (0.28)

Protein

3.70 (0.58)

3.69 (0.56)

0.01 (0.04)

3.56 (0.58)

3.53 (0.55)

-0.02 (0.05)

Lactose 4.51 (0.21) 4.52 (0.18) -0.01 (0.04) 4.47 (0.21) 4.49 (0.18) -0.02 (0.05)

  1. Diff - difference between the two udder halves

  2. * - statistical significant difference P<0.05


Increased MF raised the content of FFA in the cold stored milk (Table 2), but no effect was seen in the fresh milk. The volume based average fat globule size was significantly (P<0.01) larger in the milk collected from the UH milked four times daily (4.36 µm) compared to the UH milked two times (4.28 µm). Neither short nor long-chained fatty acids were affected. No change was observed in the activity of γ-glutamyl transpeptidase (Wiking et al., 2006). The results indicate that the increased FFA can be due to the larger fat globules, since it has been


observed that larger fat globules are more unstable than smaller globules (Wiking et al., 2003).


Table 2. FFA content (meqv./100 g fat) in milk from udder halves (UH) milked twice daily in period one and one UH was milked twice daily while the contralateral was milked four times in period two. Milk samples were stored cold (5°C) during 24 h, a.m. and p.m. milkings. Results are expressed as mean and standard deviation (SD); n=11

image

Period 1 Period 2

(control period)

1

(experimental period)

milking frequency Diff

milking frequency Diff

2 x 2 x 2 x 4 x

FFA a.m.

1.22 (0.58)

1.14 (0.41)

0.08 (0.19)

1.14 (0.46)

1.44 (0.68)

-0.30(0.24)**2

FFA p.m. 1.62 (0.62) 1.33 (0.68) 0.29 (0.98) 1.14 (0.42) 1.55 (0.77) -0.41 (0.41)**

  1. Diff - difference between the two udder halves

  2. **- statistical significant difference P<0.01


Casein content was not affected by MF neither at a.m. (2.65%) or p.m. milking (2.75%). In the milk collected during a.m. the plasminogen-derived activity decreased (P<0.01) from 99 to 83 (dA405/min/mL milk). Plasmin activity decreased both during a.m. and p.m. milking (Table 3). The results indicate that increased MF may influence protein quality. In this study no effect was detected on casein content, probably since fresh milk was analysed. It cannot be excluded that the effect of increased plasmin activity would have been detected in milk stored for more than 24 h. No significant effect was observed for proteolysis.


Table 3. Plasmin activity (dA405/min/mL milk) in udder halves (UH) milked twice daily in period one and one UH milked twice daily while the contralateral was milked four times in period two, a.m. and p.m. milkings. Results are expressed as mean and standard deviation (SD); n=11

Period 1

Period 2

(control period)

milking frequency


1

(experimental period)

milking frequency


Diff

2 x

2 x

2 x

4 x

image


Diff


Plasmin a.m. 102 (42) 95 (32) 8 (18) 103 (34) 82 (28) 21 (12)***2

Plasmin p.m. 104 (45) 104 (38) 1 (14) 113 (40) 91 (33) 22 (15)***

  1. Diff - difference between the two udder halves

  2. ***- statistical significant difference P<0.001


The decreased plasmin and plasminogen-derived activity in the more frequently milk UH could partly be explained by an improved integrity of tight junction, as indicated by the decreased content of Na and increased K in milk samples collected from the UH milked four times a day (Table 4), which agrees with Sorensen et al. (2001).


Table 4. Content of Na and K (mmol/L) in udder halves (UH) milked twice daily in period one and one UH was milked twice daily while the contralateral was milked four times in period two, a.m. and

p.m. milkings. Results are expressed as mean and standard deviation (SD); n=11

image

Period 1 Period 2

(control period)

1

(experimental period)

milking frequency Diff

milking frequency Diff

2 x 2 x 2 x 4 x

Na a.m.

16.6 (2.9)

16.4 (2.3)

0.2 (1.2)

15.1 (2.6)

14.1 (1.9)

0.9 (1.3)*2

Na p.m.

16.0 (2.7)

15.7 (2.2)

0.3 (0.9)

14.8 (2.9)

13.8 (2.0)

1.0 (1.4)*

K a.m.

41.5 (4.3)

41.5 (4.0)

0.0 (1.0)

41.8 (3.8)

42.5 (3.6)

-0.7 (0.9)*

K p.m. 41.7 (3.8) 41.7 (3.8) 0.0 (0.8) 42.5 (3.7) 43.4 (3.8) -0.9 (0.7)**

  1. Diff - difference between the two udder halves

  2. *- statistical significant difference P<0.05, ** - statistical significant difference P<0.01


    CONCLUSIONS


    Increased MF had a negative effect on content of FFA in the milk while the level of plasmin decreased, indicating that increased MF is favourable for milk protein.


    REFERENCES


    Amos H.E., Kiser T., Loewenstein M., 1985. Influence of milking frequency on productivity and reproductively efficiencies of dairy cows. J. Dairy Sci. 68, 732-739

    Bastian E.D., 1996. Plasmin in milk and dairy products: An update. Int. Dairy J. 6, 435-457 Erdman R.A., Varner M., 1995. Fixed yield responses to increased milking frequency. J. Dairy Sci.

    78, 1199-1203

    Klei L.R., Lynch J.M., Barbano D.M., Oltenacu P.A., Lednor A.J., Bandler D.K., 1997. Influence of milking frequency three times a day on milk quality. J. Dairy Sci. 80, 427-436

    Larsen L.B., Rasmussen M.D., Bjerring M., Nielsen J.H., 2004. Proteases and protein degradation in milk from cows infected with Streptococcus uberis. Int. Dairy J. 14, 899-907

    Östensson K., Hageltorn M., Åström G., 1988. Differential cell counting in fraction-collected milk from dairy cows. Acta Vet. Scand. 29, 493-500

    Sorensson A., Muir D.D., Knight C.H., 2001. Thrice-daily milking throughout lactation maintains epithelial integrity and thereby improves milk protein quality. J. Dairy Res. 68, 15-25

    Svennersten-Sjaunja K., Persson S., Wiktorsson H., 2002. The effect of milking interval on milk yield, milk composition and raw milk quality. In: Proceedings of the International Symposium. The first North American Conferences on Robotic Milking. Toronto (Canada)

    Svennersten-Sjaunja K., Wiking L., Nielsen J.H., BåviusA.-K., EdvardssonA., Larsen L.B., 2006. Effect of milking frequencies on milk protein and protein composition (Manuscript in preparation)

    Wiking L., Björck L., Nielsen J.H., 2003. Influence of feed composition on stability of fat globules during pumping of raw milk. Int. Dairy J. 13, 707-803

    Wiking L., Frost M.B., Larsen L.B., Nielsen J.H., 2002. Effects of storage conditions on lipolysis, proteolysis and sensory attributes in high quality raw milk. Milchwissenschaft 57, 4

    Wiking L., Nielsen J.H., Båvius A.-K., Edvardsson A., Svennersten-Sjaunja K., 2006. Impact of milking frequencies on the level of free fatty acids in milk, fat globule size and fatty acid composition. J. Dairy Sci. 89, 1004-1009

    Journal of Animal and Feed Sciences, 16, Suppl. 1, 2007, 156–160


    Effects of spring-calving compared to autumn- calving on the lactation curve and milk quality in Norwegian herds


    1. Schei1,2,3, O.M. Harstad1, I.J. Karlengen1, T.H. Garmo1,

      J. Ødegård1 and G. Klemetsdal1


      1Departement of Animal and Aquacultural Sciences, Norwegian University of Life Sciences

      P.O. Box 5003, 1432 Ås, Norway

      2TINE Norwegian Dairy Association

      P.O. Box 58, 1430 Ås, Norway


      ABSTRACT


      The objective of this work was to study the effects of spring calving in comparison with autumn- calving on the trajectory of both milk yield and quality (percentages of protein, fat and lactose, and also somatic cell counts (SCC) and urea). On average, autumn-calvers had 0.8 and 1.2 kg higher daily milk yield and ECM (energy-corrected milk), respectively, than those calving in the spring, due to a higher yield in mid- and late lactation. Milk fat and lactose were also higher and SCC lower for those calving in autumn, and the reduction of protein and fat percentages in early lactation was lower. These results suggest that maintaining a high milk yield is a greater challenge for spring- calving cows on pasture feeding than for autumn-calving cows fed indoors.


      KEY WORDS: lactation curve, autumn, spring, milk quality


      INTRODUCTION


      In Norway, the frequency of cows calving in spring is significantly lower than the frequency of cows calving in autumn. This has led to an imbalance between the production and demand of milk, with a lack of milk supplied during the summer. For the farmers, increased milk production at pasture through a change of period of calving, may reduce feed costs and improve milk quality (Garcia and Holmes, 2001). The objective of the present work was to study the effects of spring-calving compared with autumn-calving on milk yield and contents of milk protein, fat, lactose, somatic cell count (SCC) and urea in Norwegian dairy herds.


      image

  3. Corresponding author: e-mail: ingunn.schei@umb.no


MATERIAL AND METHODS


Individual test-day data for Norwegian Red, comprising two years (2002 to 2004) from the Norwegian Dairy Herd Recording system, were used. From these data, cows calving in April and in September were sampled to represent spring- and autumn calving, respectively. In the recording system, milk yield and concentrate supply are normally recorded for each cow monthly, whereas milk content traits (protein, fat, lactose, urea and SCC) are recorded every second month. For each group, cows with at least two observations in the period from calving until 40 weeks in milk (WIM) were kept. Protein, fat, lactose, urea and SCC were determined using an infrared milk analyser (MilkoScan, Foss Electric, Hillerød, Denmark). The dataset for milk and concentrate comprised a total of

284.544 records from 11.101 different herds and 31.121 individual lactations of which 40% calved in the spring and 60% in the autumn. The corresponding dataset for milk components contained 76.044 records. Data were analysed for fixed effects of spring- or autumn-calving, parity, WIM, interaction of region and year, and these factors interactions with calving-season by PROC GLM of the SAS software (SAS Institute Inc., Cary, USA). Analysis of SCC was based on loge

transformed test-day observations (SCS).


RESULTS


Least-square means of average daily milk yield, milk components, and concentrate supply, grouped according to calving period are presented in Table

1. The corresponding values during the lactation period, within lactation number, are shown in Figure 1. Cows calving in autumn were given on average 0.8 feed


Table 1. Least-square means of daily milk yield, ECM and milk components for spring- and autumn calving cows, respectively

image

Spring Autumn Calving-season Curvature1


mean

SEM

mean

SEM

F

P

F

P

Milk yield, kg

21.9

0.016

22.7

0.013

1651

***

84.1

***

ECM2, kg

22.1

0.039

23.3

0.030

528

***

17.6

***

Protein, %

3.35

0.002

3.33

0.002

33.5

***

33.9

***

Fat, %

4.12

0.006

4.17

0.005

31.1

***

12.5

***

Lactose, %

4.61

0.001

4.66

0.001

599

***

52.0

***

SCS3, 1000/mL

4.22 (147)4

0.009

4.05 (120)

0.007

244

***

4.5

***

Urea, mmol/L 5.1 0.010 5.0 0.008 71.2 *** 60.0 ***

1 milk yield and ECM three way interactions of calving-season × lactation number × weeks in milk, otherwise two ways excluding lactation number; 2 ECM = energy corrected milk; 3 somatic cell

4

score (loge transformed somatic cell count);

arithmetic means in brackets


image


image


image


image

image

image

image

image

image

image

image

image

image

image

image

image

image

image

image

image

image

image

image

image

FU

Spring-calving 1. lactation Autumn-calving 1. lactation

Spring-calving 2. lactation Autumn-calving 2. lactation

Spring-calving >2. lactation Autumn-calving >2. lactation


Figure 1. Least-square means of daily milk yield and concentrate supply, by calving season × lactation number × weeks in milk


units (FU) more concentrate and had a daily milk yield and ECM of 0.8 and 1.2 kg higher than the spring-calvers, respectively. Milk from autumn-calvers had also a significantly higher content of fat and lactose, and a significantly lower SCS. Calving period had no effect on the amount of concentrate offered, milk yield or milk quality during indoor feeding the first weeks of the lactation. Most of the spring-calvers turned to pasture at 4 to 6 WIM. In spite of lower concentrate supply during the first weeks at pasture, the spring-calvers maintained the milk yield at the same level as the autumn-calvers most of the period at pasture. Thus, it is during the last period at pasture and in the following indoor feeding period the spring-calvers produce less milk than the autumn-calvers. The autumn- calvers are at spring pasture in the corresponding stage of lactation. The drop in milk production of spring-calvers relative to autumn-calvers, occurred earlier for primiparous cows compared with multiparous cows (Figure 1). For milk components the interaction between calving season and lactation number were only of minor importance (1.36<F<3.39). Hence, the trajectory of milk protein


image


image

image


image

image

image

image

image

image

image

image

image

image

image

image

image

image

image

image

image

image

image

image

image

image

image

Figure 2. Least-square means of content of milk protein and fat by calving season x weeks in milk


and fat content are presented across lactation numbers (Figure 2). The milk of spring-calvers had lowest concentration of fat, but also protein in early lactation at pasture, but they were highest in late lactation. The curve for lactose had the same shape as that for milk yield (results not shown). Spring-calvers also had higher milk urea in mid lactation than did autumn-calvers (results not shown). It is also worth noting the higher SCS of spring-calving cows in mid lactation, but this will not be discussed further.


DISCUSSION


In Norway, cows are normally at pasture from May to September, the length being somewhat dependent on region. Spring-calvers will therefore be in their peak lactation (4 to 6 WIM) at the start of the grazing season. For cows calving in the autumn, most of the milk production will be based on indoor feeding and only the late lactation will be at pasture. High yield in spite of reduced supply of concentrate to spring-calved cows was probably due to high quality pastures in spring and early summer, consistent with observations in an earlier Norwegian study (Olesen et al., 1999). Garcia and Holmes (2001) also found a more peaked lactation curve of spring-calving cows than that of autumn-calving cows, the difference being due to a higher yield in peak lactation and a lower yield in mid and late lactation. However, autumn-calving cows may have a “second” peak during the following spring associated with a greater availability and quality of pasture in spring (Garcia and Homles, 1999). The variable access and quality of pasture strongly affect the shape of the lactation curve and might also result in that milk production will in some periods rely on body condition loss (Garcia and Holmes, 1999). Poor quality pasture at the end of the grazing season will probably be the main reason for the reduced milk yield for spring-calving cows in mid and late lactation. The high content of milk urea by spring-calving cows in mid lactation


may be due to a high level of non-protein nitrogen in late summer pasture, but may also indicate a lack of energy for the rumen microbes and thus, a lower utilization of the protein in the rumen. The lower milk protein content of spring-calvers in early lactation is likely attributed to deficiency of energy, and probably also of aminogenic- and glucogenic substrates, while the low milk fat content may be due to low fibre content in spring and early summer pasture.


CONCLUSIONS


In Norway, the lactation curve is more peaked for cows calving in spring than for those calving in autumn. This is due to a lower milk yield for spring-calving cows than for autumn-calving cows in late lactation. In early lactation, especially fat, but also milk protein content were lowest for spring-calvers. The results may be explained by the reduced concentrate supply and the variable access and quality of the pasture during late summer. These results suggest that it is a greater challenge to keep a high milk production in spring-calving cows on pasture, compared with indoor-fed autumn-calving cows.


REFERENCES


Garcia S.C., Holmes C.W., 1999. Effects of time of calving on the productivity of pasture-based dairy systems: A review. N. Z. J. Agr. Res. 42, 347-362

Garcia S.C., Holmes C.W., 2001. Lactation curves of autumn- and spring-calved cows in pasture based systems. Livest. Prod. Sci. 68, 189-203

Olesen I., Lindhardt E., Ebbesvik M., 1999. Effects of calving season and sire’s breeding value in dairy herd during conversion to ecological milk production. Livest. Prod. Sci. 61, 201-211