Phytase supplementation improved growth performance and bone characteristics in broilers fed varying levels of dietary calcium

An experiment was conducted to investigate the effect of dietary Ca level on the efficacy of phytase. A total of 288 male Ross x Ross 708 broilers with initial and final BW of 37 and 705 g, respectively, were used in brooder batteries from 0 to 21 d posthatch. Each treatment had 8 replications with 6 broilers/replicate pen. All diets were corn-soybean meal based and formulated to contain 1.26% total Lys. The treatments were positive control with 0.45% nonphytate P and 1% Ca and a negative control with 0.20% nonphytate P with 0.67, 1.00, or 1.33% Ca fed with or without 500 phytase units of Optiphos (Escherichia coli-derived phytase; JBS United Inc., Sheridan, IN). Increasing Ca from 0.67 to 1.33% linearly decreased (P [less-than or equal to] 0.003) ADG, ADFI, bone breaking strength, bone weight, tibia ash weight, and percentage tibia ash; however, quadratic effects were found for ADFI, G:F, percentage tibia ash, and mortality (P [less-than or equal to] 0.09). Phytase supplementation increased (P < 0.001) ADG, ADFI, bone breaking strength, bone weight, ash weight, and percentage tibia ash and decreased (P = 0.054) mortality. The increase in ADG, ADFI, bone weight, ash weight, and percentage tibia ash (P [less-than or equal to] 0.026) and decrease in mortality (phytase x Ca linear; P = 0.058) from phytase supplementation was greater in broilers fed the higher levels of Ca. Calcium utilization was linearly decreased (P < 0.002) with increasing Ca. Phosphorus digestibility and utilization were increased with increasing levels of Ca (P [less-than or equal to] 0.002); however, P utilization decreased at 1% Ca and increased at 1.33% (quadratic; P < 0.070). Phytase supplementation increased Ca utilization (P < 0.024), P digestibility (P < 0.001), and P utilization (P < 0.029). However, the increase in P digestibility (phytase x Ca; P < 0.021) was greater at the lower levels of Ca whereas P utilization (phytase x Ca; P < 0.001) was greater at 1.33% Ca with phytase supplementation. The results of this research indicate that dietary Ca level, within the ranges used in this experiment, does not negatively affect the efficacy of phytase.