Linking ileal digestible phosphorus and bone mineralization in broiler chickens fed diets supplemented with phytase and highly soluble calcium.

The objectives of this study were to deter-mine the ileal digestibility of P in potassium phosphate, phytase-related ileal digestible P release, bone-mineral-ization-based ileal digestible P equivalency of phytase, and phytase-related efficiency of ileal digestible P uti-lization for bone mineralization in broiler chickens at 2 dietary concentrations of highly soluble Ca (HSC). Birds were sorted by BW at d 15 posthatch and as-signed to 8 cages per diet with 8 birds per cage. Twelve diets were arranged in a 2 x 6 factorial of HSC at 5 or 6 g/kg and P supply treatment at 6 levels consisting of 4 added P levels (P from KH2P04 added at 0, 0.7, 1.4, or 2.1 g/kg of diet) or 2 added phytase levels (500 or 1,000 phytase units). On d 24 posthatch, ileal digesta were collected for ileal P digestibility (IPD) determina-tion and the left tibia was collected from the 4 heaviest birds in each cage for bone ash determination. Weight gain, G:F, and tibia ash were higher (P < 0.05) at 5 than at 6 g of HSC/kg. Added P from KH2P04 or add-ed phytase linearly increased (P < 0.001) weight gain, G:F, tibia ash, and IPD. The IPD of KH2P04 derived from multiple linear regressions of digestible on total P intake for the diets without added phytase showed a reduction (P < 0.05) from 89.5 to 84.5% with increased HSC from 5 to 6 g/kg. Polynomial regressions of digest-ible P intake on phytase intake indicated that 1,000 units of added phytase released 1.701 or 1.561 g of di-gestible P in diets containing 5 or 6 g of added HSC/ kg, respectively Polynomial regressions of tibia ash on digestible P or phytase intake in diets containing 5 or 6 g of added HSC/kg at 1,000 phytase units gave di-gestible P equivalency of 1.487 or 1.448 g, respectively. Thus, phytase-related efficiency of ileal digestible P uti-lization for bone mineralization was 87.4 and 92.8% in diets containing 5 or 6 g of added HSC/kg, respectively [ABSTRACT FROM AUTHOR]