Effects of Increasing Phytase Inclusion Levels on Broiler Performance, Nutrient Digestibility, and Bone Mineralization in Low-Phosphorus Diets

The objective of the current study was to evaluate the impact of increasing levels of phytase in corn-soy diets fed to male broilers. Experimental treatments included a positive control (PC) with a calculated non-phytate phosphorus (nPP) level of 0.43 and 0.39% for the starter and grower, respectively. The negative control (NC) diet included a reduction in nPP to 0.25 and 0.23% in the starter and grower, respectively, and phytase added to NC diet with increasing levels of 250, 500, 750, 1,000, 2,000, and 3,000/1,000 FTU/kg. All phytase treatments were fed throughout the study with the exception of the 3,000 FTU/kg treatment, which utilized a step-down program consisting of 3,000 FTU/kg in the starter being reduced to 1,000 FTU/kg in the grower. Treatment effects on performance, apparent metabolizable energy, apparent ileal digestibility of amino acids, phosphorus, and calcium, and bone mineralization were evaluated on days 14 and 28. The NC diet decreased feed consumption (FC) (P < 0.001), body weight (BW) (P < 0.001), and increased mortality adjusted feed conversion ratio (FCR) (P < 0.001) and mortality (P < 0.05) compared to the PC. Phytase addition improved FC, BW, FCR, and mortality. Birds fed the NC exhibited lower (P < 0.001) bone mineralization, and reduced (P < 0.05) ileal digestibility of all nutrients compared to birds fed the PC. Linear and quadratic effects were observed for tibia mineralization, and all digestibility parameters with phytase addition. High dose inclusion of phytase (2,000 and 3,000/1,000 FTU/kg) yielded the greatest improvement in bird performance, nutrient digestibility, and bone mineralization amongst treatments.