Effect of microbial phytase on nitrogen and amino acid digestibility and nitrogen retention of turkey poults fed corn-soybean meal diets.

The effect of microbial phytase on N and amino acid (AA) digestibility and N retention was investigated in a 29-d trial using 480 Nicholas Large White Turkey female poults fed corn-soybean meal diets. A 2 x 2 x 2 factorial arrangement of treatments was used with 0.45 and 0.60% nonphytate P (nP), 22.5 and 28.0% CP, and 0 and 750 U of microbial phytase/kg of diet. At 0.45% nP, adding phytase to either 22.5 or 28.0% CP diets increased BW gain (P < 0.01), and percentage (P < 0.01) and weight (P < 0.10) of toe ash; at 0.60% nP, the magnitude of the effect of phytase was less (P > 0.10) than observed for 0.45% nP and inconsistent. Apparent and true ileal digestibility of N and AA was estimated by using chromic oxide as an indicator at Day 24. At 0.45% nP, adding phytase to 22.5% CP diets tended to improve the apparent and true ileal digestibility of N and AA, except cysteine or methionine; adding phytase to 28.0% CP diets increased the digestibility of N and most of the AA (P < 0.001 to 0.10). At 0.60% nP, adding phytase to 22.5% CP diets increased the apparent and true ileal digestibility of N and all the AA (P < 0.001 to 0.10), but did not change digestibilities at 28.0% CP diets. Adding phytase also increased (P < 0.001 to 0.10) apparent ileal digestibility of DM and P at 0.45% nP for both CP diets, but only for 22.5% CP diets at 0.60% nP. The total excreta were collected at Day 27 to 29. Adding phytase to 0.45% nP diets increased apparent utilization of DM (P < 0.01 to 0.10) and retention of N (P < 0.05 to 0.10) at both CP levels; retention of P was only increased (P < 0.10) at 22.5% CP. At 0.60% nP, adding phytase increased utilization of DM (P < 0.05) and retention of N (P < 0.10) only at 22.5% CP; P retention was not affected. In summary, microbial phytase enhanced growth performance, toe ash, ileal N and AA digestibility, and apparent N and P retention.