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Disorders of Cholecaiciferol Metabolism in Old Egg-Laying Hens¹

Department of Biochemistry, School of Dentistry, Showa University, 1-5-8 Hatanodai, Shinagawa-ku, tokyo 142 ^* Kuroiso Research Laboratories of C. Itoh Feed Mills Co. Ltd., 919 Aoki, Kuroiso, Tochigi 325-01, Japan

It has been reported that the rate of cracked or soft-shelled eggs markedly increases in old laying hens. We investigated the effect of age on cholecalciferol metabolism in different age groups of laying hens. The egg production rate in hens more than 500 days old was maintained within a range of about 70% of that in young hens (230–320 days old), whereas the rate of cracked or soft-shelled eggs increased markedly with age. When kidney homogenates from the different age groups were incubated with [³H]-25-hydroxyvitamin D-3, renal 25-hydroxyvitamin D-3-1-hydroxylase activity was found to decrease markedly with age. When birds were given intravenously either [³H]-25-hydroxyvitamin D-3 or [³H]-1,25-dihydroxyvitamin D-3, the accumulation of [³H]-1,25-dihydroxyvitamin D-3 in plasma and target tissues also decreased with age. Forced molting performed in old hens restored eggshell quality. The treatment also restored, though partially, the in vivo accumulation of [³H]-1,25-dihydroxyvitamin D-3 in the target tissues. These results suggest that the increased rate of cracked or soft-shelled eggs seen in older birds is associated with disorders of vitamin D-3 metabolism.

KEY WORDS: • aging • eggshell formation • 1,25-dihydroxyvitamin D-3 • forced molting

¹ Supported in part by grants 457465 and 557433 from the Ministry of Education of Japan.

² Current address is Department of Internal Medicine, Juntendo University, 2-1-1 Hongo, Bunkyo-ku, tokyo 113, Japan.

³ To whom all correspondence should be addressed.

Manuscript received 14 August 1981.