Montecuccoli, G., Institute of Animal Science, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel
Hurwitz, S., Institute of Animal Science, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel
Cohen, A., Institute of Animal Science, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel
Bar, A., Institute of Animal Science, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel

1. 1. Duodenal calcium-binding protein (CaBP) and 25-hydroxycholecalciferol (25 HCC-1-hydroxylase) increased after the onset of gonadal activity, prior to egg laying. 2. 2. A further increase in CaBP and 25-HCC-1-hydroxylase occurred at the onset of egg laying. 3. 3. An arrest of egg production, induced by Nicarbazin, resulted in a decline in both CaBP and 25 HCC-1-hydroxylase, within 3-5 days. 4. 4. The increase in calcium absorption during the interval of shell calcification, within the egg formation cycle, was not associated with changes in either CaBP or 25 HCC-1-hydroxylase. The activity of the enzyme decreased after a one-day pause in egg laying. 5. 5. Comparable results were obtained with both chicken (Gallus domesticus) and Japanese quail (Coturnix coturnix japonica). © 1977.