POTENTIAL TO ALTER THE CONTENT AND COMPOSITION OF MILK-FAT THROUGH NUTRITION

Nutritional manipulation of the rumen ecosystem provides a strategy to alter the content and composition of milk fat. Dietary fat supplement s affect the content and composition of milk fat. The magnitude of cha nges is influenced by the degree of protection; as protection increase s, the deleterious effects fatty acids on microbial activity decreases , and biohydrogenation of C-18 unsaturated fatty acids is reduced. In addition, change is influenced by the transfer of dietary fat into mil k, which is related to fatty acid composition, degree of ruminal metab olism, and efficiency of digestion. A cascade of metabolic events invo lving specific nutrients (e.g., trans fatty acids and cyclopropene aci ds) occurs that regulates the activity of key enzymes in pathways of e ndogenous fat synthesis within the mammary gland. When cattle are fed oilseeds (e.g., canola and cotton) with >75% protection from biohydrog enation, the proportion of saturated to unsaturated fatty acids is cha nged, and the fat content of milk is increased. Human consumption of d airy products containing elevated proportions of C-18 mono-and polyuns aturated fatty acids reduces the content of cholesterol in plasma low density Lipoproteins. These fat-modified dairy products are more susce ptible to autoxidation, which can be controlled by including vitamin E in the diet of lactating cow. These products also have much less soli d fat, which improves spreadability of butter. By protecting different oilseeds from ruminal metabolism, demands for energy can be satisfied while producing milk fat that can be designed for consumer and manufa cturing requirements.