Efficacy of Vitamin D from Different Sources for Turkeys

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Abstract
Different levels of vitamin D from four different sources, namely, U.S.P. reference cod liver oil no. 2, a sardine oil fortified with fish liver oils, an irradiated animal sterol, and irradiated 7-dehydrocholesterol were fed to poults as supplements to a rickets-producing diet during the first 4 weeks of life. All supplements were fed on the basis of their A.O.A.C. chick unit potency. There were distinct differences in efficacy among the supplements, suggesting that the poult utilizes certain forms of vitamin D with degrees of efficacy that differ from the chick and in this response exhibits a higher degree of species specificity than the chick. The vitamin D of the two irradiated products was distinctly more efficacious, on the basis of chick units fed, in increasing the ash content of the bones than the vitamin D of reference cod liver oil. Comparing the results obtained over the entire range of bone ash responses, this difference in efficacy is of the order of 2 to 1. While the fortified sardine oil was measurably more efficacious than the reference cod liver oil, it gave a response curve more nearly like that of cod liver oil than like the irradiated products. It is concluded that the vitamin D potency expressed in A.O.A.C. chick units is not necessarily a true measure of the value of a vitamin D supplement for turkeys.

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