Vitamin A Requirement of Growing Birds

THE National Research Council (1960) (N.R.C.) has estimated the vitamin A requirement of all chickens 0 to 8 weeks of age to be 2,640 U.S.P. units per kilogram of feed. Later, Cornell workers (Hill et al., 1961), using Single Comb White Leghorn (S.C.W.L.) chicks, found that increasing the dietary vitamin A level from 1,322 to 2,644 U.S.P. units per kilogram produced no further weight gains. They concluded that the vitamin A requirement of the chick is approximately 1,322 U.S.P. units/kg. of diet or about 50% of the present N.R.C. estimate. Thornton and Whittet (1962) attempted to determine the influence of several factors including breed on the chick’s vitamin A requirements. Unfortunately, their lowest dietary level of the vitamin was 1,762 U.S.P. units/kg. Regardless of breed used, neither growth rate nor feed efficiency was influenced by vitamin A levels ranging up to 7,050 U.S.P. units/kg. of diet. No evidence of a…