The metabolism of calcium in temperature stressed Gallus domesticus and Meleagris gallopavo

Abstract

Calcium metabolism in the temperature stressed domestic chicken and turkey was examined by (1) studying the effects of brooding temperature, dietary phosphorus and molybdenum on bone mineralization in 10-day-old turkey poults, (2) assaying for renal 25-hydroxycholecalciferol-1-hydroxylase (25-HCC-1-hydroxylase) in one to 21-day-old poults and (3) assaying for intestinal calcium-binding activity in heat stressed laying hens. A review of pertinent data on 25-HCC-1-hydroxylase activity in heat stressed laying hens is also included. Bone mineralization (percent tibial bone ash) was significantly increased (p < .05) in 10-day-old poults brooded at 31 C versus poults brooded at 35 C. Further lowering the brooding temperature to 29 C did not significantly increase bone mineralization, however. A significant (p < .05) temperature-by-diet interaction in regard to percent bone ash occurred in one experiment when poults were brooded at 29 C and 35 C. In this experiment, poults fed 1.2 percent total phosphorus had significantly higher (p < .05) bone ash at 35 C rather than 29 C. Poults fed both 1.0 and 1.2 percent total dietary phosphorus had significantly higher (p < .05) percent bone ash than poults fed 0.6 and 0.8 percent total phosphorus. Bone ash was significantly correlated (p < .05) with serum phosphorus, but not serum calcium. Poults brooded at 35 C and fed a diet supplemented with 5 ppm molybdenum (8 ppm total) had significantly greater bone ash than poults receiving the control (non-supplemented) diet. In another experiment, there was a significant (p < .05) temperature-by-diet interaction in regard to both bone ash and serum phosphorus. Percent bone ash and serum phosphorus were both significantly lower (p < .05) in the molybdenum supplemented poults brooded at 29 C, but higher at 35 C. Renal 25-HCC-1-hydroxylase was active in poults ranging from one-day to 21-days of age. Renal 25-HCC-24-hydroxylase, however, was not active in the one-day-old poult, but was active in the 7, 14, and 21-day-old poult. Intestinal homogenates from heat-stress laying hens had significantly higher (p < .05) calcium-binding activity than homogenates from non-heat-stressed hens, probably due to vitamin D-dependent calcium-binding protein synthesized in response to increased renal 25-HCC-1-hydroxylase activity.