Dietary factors influencing calcium and phosphorus utilization by broiler chicks
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Calcium and phosphorus are the most abundant minerals in the body of animals. They are macrominerals in animal nutrition, as they are required at relatively high levels. Calcium and phosphorus absorption and metabolism are influenced by many factors, such as the levels and ratio of inclusion in the diet, vitamin D3 and its derivatives, phytase, and organic acids. The effects of the above factors are investigated in four separate battery studies. Study one investigated the effects of phytase and 1α-OHD3 on Ca, P and phytate P utilization. Supplementation of 1α-OHD3 and phytase to P-deficient corn-soybean meal and corn-peanut meal based broiler diets increased P, and phytate P utilization, as indicated by an increase in bone ash, body weight gain, plasma P, phytate P and P retention, and also reduction in incidence of P-deficiency rickets. Study two investigated the effects of combinations of phytase, methionine source, and calcium or 1α-OHD3 on phosphorus utilization in broilers. Phytase, 1α-OHD3, and HMB (an organic acid) increased phytate P utilization, and the effect of each supplement often depended on the levels of other supplements and nutrients. Study three evaluated the efficacy of several 1α-OHD3 compounds as a substitute for cholecalciferol. Slope ratio analysis of data from the measurements of 16-d BWG, plasma Ca, rickets and bone ash indicated the bioavailability of the different 1α-OHD3 (except for the 5, 6 trans 1α-OHD3 ¬ which was inactive) to be 7 to 15 times more active as compared to D3. There were differences between the 1α-OHD3 compounds due to source, processing, and cis-trans isomerism. Study four investigated the effect of lithocholic acid, a bile acid which has been reported to have vitamin D activity in rats, on commercial broiler chicks. Lithocholic acid, at low levels, had some vitamin D3 activity in chicks, as indicated by increased plasma Ca and calbindin expression. It also caused severe hepatotoxicity and growth depression to chicks.