The effects of two corn-expressed phytases on broiler growth performance and tibia mineralization

This study examined the effects of 2 corn-expressed phytases, differing in enzyme concentration within the grain (3,000 or 9,677 Fytase unit [FTU]/g), on broiler performance and tibia mineralization when used as a component in pelleted feed. Dietary treatments included a positive control (PC), with industry-recommended levels of calcium and phosphorous, and a negative control (NC), lower in calcium and nonphytate phosphorous. Six diets containing corn-expressed phytase at high or low grain concentrations, formulated to 3,000, 6,000, or 9,000 FTU/kg, were created using the NC. Diets were conditioned at 70°C for 15 s and pelleted using a 4.76 × 38.1 mm pellet die. Descriptive enzyme recovery after pelleting (58–360%) and mixer CV based on enzyme activity (8–24%) demonstrated variability with the phytase assay and did not show trends across treatment main effects. Diets were fed to Hubbard × Ross 708 (n = 1,632) male broilers for 39 d. On day 21, five birds/pen were euthanized, and tibiae were excised to determine tibia mineralization. Treatments were arranged in a 2 (corn-phytase product) × 3 (phytase inclusion) factorial in a randomized complete block design. Broilers fed the NC had increased day 0–39 feed conversion ratio (FCR) compared with all other treatments (P < 0.05). Broilers provided PC and NC produced expected differences in tibia ash as a percentage or as mg/bird (P < 0.05). While there were no differences between phytase products, birds that were fed a phytase inclusion of 9,000 FTU/kg had higher tibia ash/bird and tibia ash percentage (P < 0.05). This study demonstrates that corn-expressed phytases can improve day 21 tibia mineralization and day 0 to 39 FCR, regardless of concentration in the grain.