Energy releasing efficacy of graded levels of a commercial microbial phytase

SUMMARY: An experiment was conducted to determine the energy release of a commercial phytase fed to broilers at multiple doses in basal diets that varied in ME. Dietary treatments included 3 negative controls (NC; 0.75% calcium and 0.30% non-phytate phosphorus) formulated at 3 ME levels (2,701, 2,868, and 3,000 kcal/kg). A commercial phytase product was added to each NC diet at 1,500, 4,500, 13,500, and 30,000 FTU/kg, creating a total of 15 dietary treatments. The phytase utilized was a phytase sourced from an Escherichia coli species bacterium expressed in a Trichoderma reesei fungus. Treatments were arranged in a 5 (phytase dose) × 3 (ME level) factorial in a randomized complete block design with 9 replications of 10 male broilers fed each of 15 dietary treatments for 21 d. On d 7, 14, and 21, birds provided the 3,000 kcal/kg diet had the lowest bird FI, and birds provided the 2,701 and 2,868 kcal/kg diets had the highest (P < 0.001). Additionally, FCR decreased as ME increased (P < 0.0001). Trends were observed for ME level × phytase dose interactions for d14 and 21 FCR. These trends demonstrate that phytase was most beneficial with the low energy diets. Eight treatments were selected for apparent ileal digestible energy (AIDE) analysis based on d 14 and 21 FCR data; AIDE ranged from 2,816 to 3,485 kcal/kg. Contrary to past studies, clear results were not observed for the energy releasing efficacy of graded levels of phytase. Performance improvements with phytase supplementation were likely more associated with P availability than AIDE