IONIC AND ENDOCRINE CHARACTERISTICS OF REPRODUCTIVE FAILURE IN CALCIUM-DEFICIENT AND VITAMIN D-DEFICIENT LAYING HENS

Whole blood ionized calcium and plasma total calcium, inorganic phosphorus, estradiol-17-beta, progesterone, and 1,25-di-hydroxycholecalciferol concentrations were measured in calcium- or vitamin D-deficient Single Comb White Leghorn hens. Control birds were serially sampled every 2 h for 26 h immediately following oviposition until the next oviposition. Deficient birds, which had ceased laying 10 to 14 days prior to sampling, were sampled at the same times. The control birds had significantly higher mean total and bound plasma calcium and inorganic phosphorus concentrations than the deficient hens. Control and vitamin D-deficient hens had similar mean ionized calcium concentrations. Control hens exhibited a cyclic pattern in ionized calcium and inorganic phosphorus concentrations over the sampling period that was related to shell calcification. Deficient hens showed no changes in ionized calcium concentration during this time. Plasma 1,25-dihydroxycholecalciferol concentrations were significantly higher in the calcium-deficient birds than the control or vitamin D-deficient hens. Mean plasma estradiol-17-beta and progesterone concentrations were consistently higher in the control hens than the deficient hens. Consistent with this observation were decreases in ovary and oviduct weights, which occurred in the nonlaying deficient hens.