Effect of Dietary Phosphorus Level and Phytase Enzymes on Broiler Performance and Bone Mineralization
Type of Degreedissertation
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A series of experiments evaluated dietary levels of non-phytate phosphorus (npP), with or without phytase enzyme supplementation in corn-soybean meal diets, on growth and skeletal performance in the broiler chicken. A preliminary experiment determined that muscle and flesh removal from bone was not required to adequately assess tibia breaking force. The first experiment investigated the effects of dietary npP concentration, maternal flock age, and bird sex on live performance. Body weight and bone strength were improved by higher concentrations of dietary npP, an increase in breeder flock age, and in male broilers. Experiment two evaluated the effects of three commercial phytase enzymes included into a 0.25% npP diet. Enzyme use improved body weight and bone strength, while decreasing overall mortality, in comparison to the unsupplemented diet. A third experiment investigated the effects of two phytase enzymes in a 0.35% npP diet on the performance of two commercial broiler strains. Results indicated no differences in body weight or bone strength between the two strains. Similar to Experiment 2, enzyme usage led to improvements in performance and bone strength in comparison to the unsupplemented diet. Two final experiments were implemented to assess the effects of phytase enzyme supplementation on birds undergoing an induced challenge with Eimeria spp. Birds were challenged or unchallenged and subjected to one of three coccidiosis control strategies: vaccination, iii feed coccidiostat, or none. Data from both experiments confirm that phytase supplementation may release an equivalence of 0.20% npP when dietary Ca and npP are adjusted accordingly. Birds undergoing a coccidiosis challenge had reduced performance and decreased bone strength when not provided phytase supplementation. In addition, coccidiosis control programs provided improvements in bird performance and decreased incidence of coccidiosis. In Experiment 5 immune function was also assessed via cytokine production. Results indicated that IFN-γ and IL-17 expression was most likely 18 d following exposure to Eimeria spp. These experiments conclude that phytase supplementation of low and marginal npP diets may lead to improvements in growth and skeletal performance and may have an effect on incidence of infection and immune function in growing broiler chickens.