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Hydroxylation of Carbon-24 of 25-Hydroxycholecalciferol Is Not Necessary for Normal Embryonic Development in Chickens¹

Department of Biochemistry, University of Wisconsin-Madison, College of Agricultural and Life Sciences, Madison, WI 53706 ^* Pharmaceutical Chemistry, Faculty of Pharmaceutical Sciences, Teikyo University, Sagamiko, Kanagawa 199-01, Japan

Laying hens fed 25-hydroxycholecalciferol, 24,24-difluoro-25-hydroxycholecalciferol, 1,25-hydroxycholecalciferol or 24,25-hydroxycholecalciferol 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 When the hens were 40 weeks old, 25-hydroxycholecalciferol was withdrawn and egg production ceased in 4 weeks.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 µg of 25-hydroxycholecalciferol, 2.0 µg of 24,24-difluoro-25-hydroxycholecalciferol, 0.4 µg of 1,25-dihydroxycholecalciferol, 2.0 µg 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).

KEY WORDS: • cholecalciferol • chick embryo development • calcium • egg • hatchability

¹ This work was supported by Program Project Grant No. AM-14881 from the National Institute of arthritis, Diabetes, Digestive and Kidney Diseases of the National Institutes of Health and by the Harry Steenbock Research Fund of the Wisconsin Alumni Research Foundation.

² No reprints will be available from the authors, H. F. D. for correspondence.

Manuscript received 13 April 1984.