Studies on the role of 1,25-dihydroxyvitamin D in chick embryonic development.

Vitamin D-deficient laying hens were repleted with 25-hydroxy[26,27-3H]vitamin D3 or 1,25-dihydroxy[26,27-3H]vitamin D3. Egg production returned to normal for both groups of hens by the third week. Eggs from hens fed either 25-hydroxy[26,27-3H]vitamin D3 or 1,25-dihydroxy[26,27-3H]vitamin D3 contained 1,25-dihydroxy[26,27-3H]vitamin D3. Eggs from hens fed 25-hydroxy[26,27-3H]vitamin D3 contained substantial amounts of 25-hydroxy[26,27-3H]vitamin D3, while those from hens fed 1,25-dihydroxy[26,27-3H]vitamin D3 contained none. Plasma from 18-day embryos from hens fed 1,25-dihydroxy[26,27-3H]vitamin D3 contained little or no 1,25-dihydroxy[26,27-3H]vitamin D3, while that from 18-day embryos from hens given 25-hydroxy[26,27-3H]vitamin D3 had normal levels of 1,25-dihydroxy[26,27-3H]vitamin D3. No eggs from hens fed 1,25-dihydroxy[26,27-3H]vitamin D3 hatched, while eggs from hens fed 25-hydroxy[26,27-3H]vitamin D3 achieved a hatchability of 90%. It appears that embryos from hens maintained on 1,25-dihydroxyvitamin D3 as their sole source of vitamin D are essentially vitamin D deficient.