Multiexperiment evaluation of increasing phytase activity from Optiphos® and Optiphos Plus® on 21-day broiler performance and tibia mineralization

SUMMARY: Phytase is used in nearly all broiler diets at varying levels and new commercial sources have been developed in recent years. A series of 5 experiments at 4 different universities were conducted to investigate broiler performance metrics and tibia mineralization from 2 mixer-added, Escherichia coli-derived, 6-phytases, Optiphos, a coated phytase, and Optiphos Plus, a recently developed phytase product selected to be intrinsically heat stable, independent of a coating. Treatments for each experiment included a negative control (NC) and the NC + varying levels of Optiphos and Optiphos Plus up to 1,500 FTU/kg. Experimental diets were fed to male broiler chicks for 21 d. On d 21, broilers were euthanized and tibiae were excised to determine tibia mineralization. Experiments 1–4 utilized pelleted diets while Experiment 5 utilized a mash diet. For each experiment, treatments were arranged by a formulated phytase level and source factorial, using a randomized complete block design. In addition, slope-ratio models were created using data from all experiments to evaluate responses to analyzed phytase levels. Positive live performance and tibia mineralization responses to phytase activity were observed (P < 0.05) in all 5 experiments. Performance and bone mineral metrics continued to improve up to approximately 1,500 FTU/kg in a curvilinear fashion, demonstrating a value of super-dosing, the degree employed being dependent on the product used and the cost-benefit economics of implementation. When comparing nonlinear response slopes across all analyzed phytase levels and experiments, the data showed that efficacy of Optiphos Plus was approximately 20% higher than that of Optiphos at similar analyzed levels (P < 0.05)