Evaluation of exogenous phytase in high-phytate diets for broiler chickens and pigs

There is a gap in the understanding of the relationship between dietary phytate levels and the relative efficacy of phytase to improve amino acid (AA) digestibility in pigs and chickens. Two experiments were conducted to investigate the effect of exogenous phytase on standardized ileal digestibility (SID) of AA and the apparent ileal digestibility (AID) of P in both standard- (SP) and high-phytate (HP) diets for broilers and swine. There were either 40 cages of Cobb 500 male broilers or 10 crossbred barrows (35 kg) fitted with ileal T-cannulas. Both studies were allotted to five dietary treatments (8 replicates). Treatments consisted of four corn-soybean meal-based diets arranged in a 2 × 2 factorial of standard or high phytate and exogenous phytase at 0 or 1 000 phytase units (FYT)/kg; and one N-free diet. Birds were fed a common starter diet from d 0 to 20 and fed experimental diets from d 20 to 25. Birds were euthanized on d 25 via CO₂ asphyxiation, and digesta were collected from the terminal ileum. Pigs were fed for a total of four 7-d periods, where digesta were collected on d 6 and 7 of each period. Diet and digesta samples were analyzed for DM, N, Ti, AA, and P to determine AA and P digestibility. The SID of AA was determined by correcting the AID of AA for the basal endogenous losses estimated using the N-free diet. Main effects of the diet type (standard or HP) and phytase (0 or 1 000 FYT/kg), and the interaction of diet type and phytase were evaluated. For both experiments, the HP diets produced lower SID of AA compared to the SP (P < 0.001). For broilers, there was a phytase effect (P < 0.001) for the SID of all AAs evaluated regardless of the diet type. For pigs, phytase improved (P < 0.05) the SID of Met, Lys, Cys, Glu and Ser and tended to improve (P < 0.10) Arg, Leu, Thr, and Tyr. There were no significant interactions for either experiment. For both experiments, AID of P was lower for the HP diets (P < 0.01), and phytase produced greater AID of P for both diet types (P < 0.01). These data indicate that phytase greatly improves the digestibility of P for broilers and pigs and has the ability to significantly increase the digestibility of amino acids for these animals, regardless of the dietary phytate P.