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Milk compositional quality and the rôle of forages
Published online by Cambridge University Press: 27 February 2018
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In most experiments in which the influence of forage to concentrate ratios on milk quality have been examined, the composition of the forage has been incidental to the purpose of the trial. Legumes have resulted in higher yields of milk than grasses of similar digestibility. However, these increases were a reflexion of higher outputs of protein and lactose, since the feeding of legumes resulted in lower contents of milk fat. Changes in the digestibility of forage have shown considerable variability in response, in terms of the concentration of milk solids. However, an increase in digestibility of forage has not resulted in decreases in the yield of fat and, further, the yield of protein has been increased.
There is no indication that there is a requirement for ‘long hay’ to maintain milk quality and that a reduction in the chop length of silage has any influence on milk composition. However, the fine grinding of grass, which was the sole forage component of the diet, has caused a marked decrease in milk fat content. This effect was not apparent when finely ground and pelleted dried grass was used as a supplement but only in ad libitum feeding regimes.
Attempts to increase the content of milk fat in May and June by the supplementation of grazed grass with small quantities of hay have had little influence on milk yield and fat content. A much greater effect was observed when grazing was restricted and silage offered ad libitum overnight. The increase in fat content may be overcome by a reduction in milk and protein yield.
In general, the changes in milk composition have been small and this is likely to be a result of the high proportion of forage in the diets examined. The quantification of response in yield and content of fat and protein to changes in forage composition requires a change in approach. More emphasis should be given to the examination of the interaction between level or type of concentrate and the composition of the forage. Further, these trials should be accompanied by experiments to examine the effects of the dietary changes on the end products of digestion.
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- Copyright © British Society of Animal Production 1984
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