Utilization of phytate and nonphytate phosphorus in chicks as affected by source and amount of vitamin D3
1997
Biehl, R.R. | Baker, D.H.
Commercial and laboratory-strain crossbred chicks responded (P < .01) markedly to 1 alpha-hydroxycholecalciferol (1 alpha-OH D3) during the 2nd and 3rd wk of life. Bone-ash responses exceeded 50% when this compound was added at 20 micrograms/kg to phosphorus (P)-deficient corn-soybean meal diets containing surfeit levels (25 micrograms/kg) of cholecalciferol (D3). Phosphorus excretion was decreased (P < .01 and, thus, retention was increased (P < .01) when l alpha-OH D3 was supplemented. A P-deficient (.10% P) casein-amino acid purified diet, devoid of D3, was used to determine whether 15 micrograms/kg of D3 was sufficient to facilitate optimal absorption of the nonphytate P contained in this diet. Bone ash responded to .075% P addition (KH2PO4), and chicks fed diets with .175% nonphytate P exhibited further bone-ash responses to 15 micrograms/kg of D3 or 10 micrograms/kg 1 alpha-OH D3. Higher levels of either of these D3 compounds did not produce additional responses. This suggested that 15 to 25 micrograms/kg of D3 in a P-deficient corn-soybean meal diet (.28% phytate P and .14% nonphytate P) is more than adequate to facilitate optimal absorption of the nonphytate P present in the diet. A P-deficient casein-dextrose diet (.13% nonphytate P and 15 micrograms/kg D3) was fed in the final chick assay, and chicks fed this diet did not show bone ash responses to 1 alpha-OH D3 or to microbial-derived phytase (1,470 units/kg). Thus, with P-deficient corn-soybean meal diets containing at least 15 micrograms D3/kg, l alpha-OH D3 supplementation markedly increased weight gain and bone ash because it increased the utilization of phytate P.
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