MILK LIPIDS

I

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.