Vitamin A Activity of Milk as Related to Pasture and Feeding Practices in Alabama

The chief source of vitamin A for livestock is the yellow pigment, carotene, which occurs in greatest abundance in pasture crops and to a Iesscr extent in hay and silage. Guilbert, Miller and Hughes (6) have concluded that about 25 micrograms of carotene per kg. of body weight represents the minimum requirement for cattle, sheep and swine. They suggest, however, that the practical minimum is 5 to 10 times the physiological minimum. Converse and Meigs (2) state that for normal calving, cows should receive 80 to 100 milligrams of carotene daily during the last months of gestation. Ward, Bechdel and Guerrant (15) have concluded that the daily carotene requirement of growing calves is 11 micrograms per pound of body weight. For the production of milk rich in vitamin A, however, the carotene requirement of dairy cattle is greatly increased. This is accentuated by the very low percentage transfer of carotene to the milk, which has been reported to range from 2.38 to 2.67 per cent (4) and from 0.14 to 0.72 per cent (9).