MILK LIPIDS Holstein Ayrshire Figure 3. 1 Range of fat content in the milk of individual cows of four breeds( from Jenness and Patton, 1959) synthesizing ability of the mammary tissue; the effect is clear-cut in the case of clinical mastitis but is less so for subclinical infection Milk yield is reduced by underfeeding but the concentration of fat usuall increases, with little effect on the amount of fat produced. Diets low in roughage have a marked depressing effect on the fat content of milk, with little effect on milk yield. Ruminants synthesize milk fat mainly from carbohydrate-derived precursors; addition of fat to the diet usually cause slight increases in the yield of both milk and fat, with little effect on fat content of milk. Feeding of some fish oils (e.g. cod liver oil, in an effort to ease the concentrations of vitamins A and d in milk) has a very marked (c. 25%)depressing effect on the fat content of milk, apparently due to the high level of polyunsaturated fatty acids( the effect is eliminated by hydr genation), although oils from some fish species do not cause this effectI MILK LIPIDS 35 - 30 - B f - 25- 0 % 3 - S s 20- r 0 15- 2 10 - 5- 69 Percentage fat Figure 3.1 Range of fat content in the milk of individual cows of four breeds (from Jenness and Patton, 1959). synthesizing ability of the mammary tissue; the effect is clear-cut in the case of clinical mastitis but is less so for subclinical infection. Milk yield is reduced by underfeeding but the concentration of fat usually increases, with little effect on the amount of fat produced. Diets low in roughage have a marked depressing effect on the fat content of milk, with little effect on milk yield. Ruminants synthesize milk fat mainly from carbohydrate-derived precursors; addition of fat to the diet usually causes slight increases in the yield of both milk and fat, with little effect on fat content of milk. Feeding of some fish oils (e.g. cod liver oil, in an effort to increase the concentrations of vitamins A and D in milk) has a very marked (c. 25%) depressing effect on the fat content of milk, apparently due to the high level of polyunsaturated fatty acids (the effect is eliminated by hydro￾genation), although oils from some fish species do not cause this effect