The essentiality of vitamin D metabolites for embryonic chick development.

Laying hens maintained on 1,25-dihydroxyvitamin D3 as their sole source of vitamin D produce eggs which appear normal but which produce embryos having a defective upper mandible and which die at 18 to 19 days of embryonic life. Hens maintained on 25-hydroxyvitamin D3, on the other hand, produce normal embryos. Hens fed a vitamin D deficient diet produce eggs which develop the same embryonic defect. Injection of the affected eggs from the 1,25-dihydroxyvitamin D3 fed hens with vitamin D3, 25-hydroxyvitamin D3, or 1,25-dihydroxyvitamin D3 greatly increases the percentage of normal embryos. It therefore appears that 1,25-dihydroxyvitamin D3 is not transferred from hen to egg in sufficient amounts to support embryonic development and that vitamin D or its metabolites, or both, are necessary for normal chick embryo development.