Hydroxylation of carbon-24 of 25-hydroxycholecalciferol is not necessary for normal embryonic development in chickens

Laying hens fed 25-hydroxycholecalciferol, 24,24-difluoro-25-hydroxycholecalciferol, 1,25-dihydroxycholecalciferol or 24,25-dihydroxycholecalciferol were used to investigate whether hydroxylation of C-24 of cholecalciferol is necessary for normal embryonic development in chickens. Laying hens were fed a rachitogenic diet and 25-hydroxycholecalciferol from hatching until normal egg production, fertility and hatchability were achieved. When the hens were 40 weeks old, 25-hydroxycholecalciferol was withdrawn and egg production ceased in 4 weeks. The hens were divided into 6 groups of 5 and dosed daily for 19 weeks with either 2.0 micrograms of 25-hydroxycholecalciferol, 2.0 micrograms of 24,24-difluoro-25-hydroxycholecalciferol, 0.4 microgram of 1,25-dihydroxycholecalciferol, 2.0 micrograms of 24,25-dihydroxycholecalciferol, both 1,25-dihydroxycholecalciferol and 24,25-dihydroxycholecalciferol or vehicle only. Egg production during this period was high for all hens fed the cholecalciferol compounds. Egg production of 3% occurred in hens given vehicle only. Fertility was over 90% for all groups of cholecalciferol compound-fed hens. Hatchability of over 90% was achieved with the eggs from hens given 25-hydroxycholecalciferol or 24,24-difluoro-25-hydroxycholecalciferol and 6% with eggs from hens fed both 1,25-dihydroxycholecalciferol and 24,25-dihydroxycholecalciferol. No eggs from hens fed 1,25-dihydroxycholecalciferol or 24,25-dihydroxycholecalciferol alone hatched (over 140 eggs in each group.