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Institute of Animal Science, Agricultural Research Organization, The Volcani Center, Bet Dagan, Israel
Changes in intestinal calcium absorption, calcium deposition into egg shell, and intestinal, renal and uterine calcium-binding protein (CaBP) in laying hens were related to changes in 25 hydroxycholecalciferol-1-hydroxylase activity (1-hydroxylase), or to the supplementation of 1
-hydroxycholecalciferol (1
-OH-CC). The onset of egg production resulted in an increased kidney 1-hydroxylase activity and intestinal and uterine CaBP. Renal concentrations of CaBP remained unchanged. Intestinal calcium and phosphorus absorption, during the period of egg shell formation, and duodenal calcium-binding protein (CaBP), were higher in 1
-OH-CC-fed than in cholecalciferol-fed hens. Renal or uterine CaBP and calcium deposition into the egg shell did not fluctuate with the vitamin D source or concentration. 1
-OH-CC injection into non-laying Nicarbazinfed hens resulted in an increase in intestinal but not renal or uterine CaBP concentrations. It is suggested that (a) CaBP in various organs responded independently to the same stimuli; and (b) calcium deposition into egg shell and uterine CaBP level are not related to kidney 1-hydroxylase activity or concentration of 1,25 dihydroxycholecalciferol.
KEY WORDS: laying hens calcium transport calcium-binding protein 25 hydroxycholecalciferol-1-hydroxylase 1
-hydroxycholecalciferol
1 Contribution from the Agricultural Research Orgauization. The Volcant Center, Bet Dagan, Israel. 1977 Series, No. 219-E. Supported by the Poultry Marketing Board of Israel.
Manuscript received 18 October 1977.