The effect of sunflower oil on the fatty acid composition of the milk of cows fed either a fat-depressing diet or grass silage

Feeding and milk protein production

This paper reviews the effects of feeding on milk protein production. It deals, first, with the chemical composition of the milk proteins and the extent to which the composition is influenced by diet, the synthesis of proteins in the mammary gland and the effects of variations in the supply of amino acids and of the energy-yielding nutrients that are absorbed from the gastrointestinal tract. There is then an examination of the impact of changes in dietary energy and protein supply on the content and yield of protein in milk and specific consideration of particular features of ration formulation, including supplementary energy concentrate foods, supplementary lipids and amount and type of supplementary protein foods. Finally, it is argued that the effects of diet on milk protein production are evaluated best simply in terms of milk protein yield; some of the pitfalls of interpreting information on milk protein content in practice are pointed out.

It is concluded that the yield of milk protein is determined by the dietary supply of energy-yielding constituents and protein but that presently employed systems for ration formulation do not provide a satisfactory means of interrelating milk protein yield and the intake of nutrients in the cow's diet.

Effect of inclusion of different forms of dietary fatty acid on the yield and composition of cow's milk

In addition to a control diet, lactating cows were offered saturated fatty acid mixtures in three forms, free acids, free triglycerides and protected triglycerides, i.e. triglyceride encapsulated within a protein matrix which was cross linked by exposure to formaldehyde. Relative to the control diet, all three supplements increased milk yield. However, only the free fatty acids gave rise to increased yields of the three major milk components. The free fat and the protected fat caused significant increases only in the lactose yield. The different effects of the supplements on the yield of milk fat are suggested to be due to the types of long chain acid reaching the mammary gland rather than to any change in rumen activity. Changes in the concentrations of the soluble multivalent ionic constituents of the milks were consistent with this conclusion.

Fat supplementation in animal production--ruminants

The effect of adding fat to the diet of the ruminant is a very complex subject. For animals with a low production potential, the role of fat is probably limited but, as the potential output is increased, energy intake becomes a more important limiting factor and the use of more fat may then be justified. If this is so, certain problems require solution. These include the effects on food intake and its metabolizability and the ME value to be assigned to the fat itself. In dairy cows, the best way to feed fat, either early in lactation or throughout, needs to be assessed together with any effects in later lactations. Finally, the best form of fat to use and the method of incorporating it into the diet also needs to be investigated.