Regulation of Intestinal Calcium Absorption in the Laying Quail: Independent of Kidney Vitamin D Hydroxylation

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Abstract
Two experiments were carried out with laying quail (Coturnix coturnix japonica) fed either cholecalciferol (40 µg/kg) or 1 α-hydroxycholecalciferol (8 µg/kg). Recovery following vitamin D depletion, as indicated by egg production and shell deposition, was faster in quail fed 1 α-hydroxycholecalciferol than in those fed cholecalciferol. Overall intestinal calcium absorption was higher in the 1 α-hydroxycholecalciferol-fed quail due to a higher absorption in the middle parts of the small intestine. This was associated with corresponding differences in the concentration of calcium binding protein. Intestinal calcium absorption was markedly higher during periods of shell formation than during periods of uterine inactivity in quail fed either cholecalciferol or 1 α-hydroxycholecalciferol. It is suggested, therefore, that the mechanism responsible for this difference is independent of vitamin D hydroxylation in the kidney.