Responses of pigs to Aspergillus niger phytase supplementation of low-protein or high-phytin diets

Growth and N utilization responses of pigs to Aspergillus niger phytase supplementation of low-protein or high-phytin diets were examined in 2 experiments. In the first experiment, 6 diets arranged in a 3 x 2 factorial with Aspergillus niger phytase at 0, 600, or 1,200 units/kg and dietary protein at 160 or 200 g/kg; and 12 pigs (growth) or 6 pigs (N utilization) per diet were used to test the hypothesis that phytase ameliorates dietary protein effects on growth and nutrient balance. In the second experiment, 4 diets arranged in a 2 x 2 factorial of phytase at 0 or 1,200 units/kg and phytin P at 2.2 g/kg (3.2 g/kg of total P) or 3.9 g/kg (4.9 g/kg of total P); and 12 pigs (growth) or 8 pigs fitted with ileal T-cannulas in a replicated 4 x 4 Latin square (for ileal digestibility of AA) per diet were used to test the hypothesis that increased phy-tin depresses nutrient utilization and phytase addition ameliorates these effects. Whereas reduced dietary protein depressed (P < 0.001) BW gain and N utilization, phytase in low-protein diet did not alleviate these effects. Although phytase ameliorated phytin-induced reduction in ileal P digestibility (P < 0.001), this was not accompanied by any change in ileal AA digestibility. Given that phytase improved (P < 0.001) P, but not N utilization of diets fed in both studies, phytase-induced improvement in BW gain of pigs fed low-phytin P diets is independent of changes in N utilization.