Protein utilization and amino acid digestibility of canola meal in response to phytase in broiler chickens

The regression method was used in a 14-d broiler chicken study to determine the true ileal digestibility of amino acid (AA) and protein utilization in canola meal (CM, 388 g of CP/kg) without or with added phytase. Experimental treatments consisted of 2 factors, phytase at 2 levels (0 or 1,500 phytase units/kg) and CM at 3 levels (125, 250, or 375 g/kg). Birds received a standard starter diet from d 1 to 8 and the assay diets from d 8 to 22 posthatch. On d 8, a total of 384 birds were allocated to 6 dietary treatments in a randomized complete block design; excreta were collected from d 12 to 14 and d 19 to 21, and ileal digesta were collected on d 22 posthatch. True ileal indispensable AA digestibility of CM were derived from the regression of AA flow (mg/kg of DM intake) at the terminal ileum against the intake of AA (mg/kg of dietary DM) of birds fed diets without or with phytase. Body weight gain (BWG), protein gain, and protein intake increased linearly (P < 0.001) with increasing CM level, regardless of phytase supplementation. Effects of phytase (P < 0.05) were observed on BWG and the protein efficiency ratio from d 8 to 15, whereas effects of phytase (P < 0.05) were observed on BWG and protein gain from d 15 to 22. There was no effect of phytase on protein intake and net protein utilization from d 8 to 22. Phytase supplementation at 1,500 phytase units/kg did not affect true ileal digestibility of any AA in CM. In conclusion, the results of this study indicated that phytase supplementation improved the protein efficiency ratio of birds fed diets containing CM as the sole protein source from d 8 to 15 posthatch but did not affect the true ileal digestibility of AA in CM as determined by the regression method.