ON SITE OF DISCRIMINATION OF CHICKS AGAINST VITAMIN D2

Chicks are capable of converting both vitamins D2 and D3 at approximately equal rates to the biologically active polar metabolite (peak IV) believed to be the metabolically active form of the vitamin. However, the peak IV metabolite from vitamin D2 has little vitamin D activity in chicks while that from D3 is more biologically active than D3 itself. The peak IV both from D2 and from D3 is fully antirachitic in rats suggesting that the chick discriminates against vitamin D2 at the level of the peak IV metabolite. © 1969.