Effect of dietary unsaturated fatty acids in various forms on the de novo synthesis of fatty acids in the bovine mammary gland.

Free and protected soya oil and soya oil fatty acids were included in the rations of dairy cows and from outputs in the milk of 18:1 trans and of polyunsaturated acids conditions in the rumen have been deduced. Similarly, the content of citrate in the milk has been used to evaluate changes occurring in the synthesis of fatty acids in the mammary gland.

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.

Effects of concentrates with beef tallow on food intake and milk production of cows fed grass silage.

In two experiments, dairy cows were given either high-quality grass silage alone or with barley-based concentrates added. Up to 946 g/day of beef tallow was added to the concentrates. Addition of tallow did not have large effects on replacement rate of concentrates until the largest amount was reached. In each experiment, addition of the least amount of tallow, 364 or 412 g/day, increased milk yield and milk fat yield, but there was no further increase as amount of tallow increased. Addition of tallow increased the proportion of metabolizable energy surplus to maintenance that was transferred into the milk. The proportion of short-chain and of 16-carbon fatty acids in milk fat was reduced and that of 18-carbon fatty acids was increased.

Effect of feeding fat to dairy cows receiving a fat-deficient basal diet. I. Milk yield and composition.

The effects of supplementing a basal diet, in which the low level of fatty acids limited milk production, with soya oil, a palm oil/palmitic acid mixture and tallow, on the yield of milk and of its constituents, and on the composition of the milk, are reported. The yields of milk and milk fat were greatly increased by all the oil-supplemented diets; the mean daily yield of solids-not-fat (SNF) was also increased, but supplementation with soya oil caused the yield of crude protein (CP) to decrease, whereas the other fat-rich concentrate mixtures gave the same mean yield of protein as did the low-fat, control diet. All 3 oil-supplemented diets lowered the proportion of CP in the milk, but the SNF content was unchanged by any treatment. Dietary soya oil tended to lower the proportion of fat in the milk, whilst the palm oil/palmitic acid mixture raised it, with the tallow exerting no effect. The results are discussed in relation to previous work in which these dietary oils have been used, but in which the intake of fatty acids from the control diets did not limit milk production to the extent reported here.

Effect of feeding fat to dairy cows receiving a fat-deficient basal diet. II. Fatty acid composition of the milk fat.

The effects on the fatty acid composition of milk fat of feeding various oil-enriched diets (soya oil, red palm oil/palmitic acid and tallow) to dairy cows receiving a fat-deficient basal diet are reported. It was found that a linear relation was obtained between the dietary intake of C18 fatty acids and their output in milk fat. A similar relation, applicable only to the oil-rich diets, was found for the C16 acids. The significance of these relations is discussed. Fatty acid compositions and yields are discussed and compared with literature examples in which similar oil-rich diets were fed, but in which the low amount of fat in the basal diet did not markedly depress milk yield. The proportion of trans-isomer in the octadecnoic acid was found to increase appreciably on feeding soya oil, and to a lesser extent with dietary tallow. A linear relation between the 18:0 and 18:1 contents of milk fat was found, and its significance is discussed.