Fat supplementation: implication in dairy cattle

Supplementation of fat or oil in the ration of high yielding dairy cattle increases the energy density of the ration without altering the composition of the other ingredients. A high proportion of free fatty acids in vegetable fat possibly improves fat digestibility in the total gastroin-testinal tract and has been associated with variable effects on milk yield and milk fat composition. Vegetable fats are rich sources of essential fatty acids, viz. linoleic and linolenic acid, and varying amounts of monounsaturated oleic acid. Polyunsaturated fatty acids (PUFAs) in die-tary fat are important substrates for the synthesis of reproductive hormones and prostaglandins and to aug-ment the reproductive performance through stimulation of the growth of ovarian follicles, increase in follicle size and number, and increased function of corpus luteum (CL) in cattle. PUFA undergoes biohydrogenation in the rumen to produce conjugated linoleic acid (CLA). The milk CLA is identified to reduce body fat levels, im-prove glycaemic profile, resynthesize glycogen, modulate immune function, improve bone mineralization, prevent heart diseases, atherosclerosis, diabetes and cancer in humans. Significantly higher levels of fat/oil (>3%, generally) in the diet may adversely affect the fermen-tation pattern through adverse effects on fibrolytic bacteria and protozoa in the rumen, subsequently low-ering the fibre and dry matter digestibility. To minimize the effect of higher levels of fat on rumen fermentation, fat may be supplied in a protected form that escapes rumen fermentation and is subsequently utilized in the lower digestive tract of high-yielding dairy cattle to pro-duce beneficial effects.