Amino acid and mineral digestibility, bone ash, and plasma inositol is increased by including microbial phytase in diets for growing pigs

The effect of microbial phytase on amino acid and energy digestibility is not consistent in pigs, which may be related to the phytase dosage or the adaptation length to the diet. Therefore, an experiment was conducted to test the hypotheses that increasing dietary phytase after an 18-day adaptation period: 1) increases nutrient and energy digestibility; 2) increases plasma P, plasma inositol, and bone ash of young pigs; and 3) demonstrates that maximum phytate degradation requires more phytase than maximum P digestibility. Data indicated that increasing inclusion of phytase [0, 250, 500, 1,000, 2,000, and 4,000 phytase units (FTU)/kg feed] in corn-soybean meal-based diets increased apparent ileal digestibility (AID) of Trp (quadratic; P < 0.05), and of Lys and Thr (linear; P < 0.05), and tended to increase AID of Met (linear; P < 0.10). Increasing dietary phytase also increased AID and apparent total tract digestibility (ATTD) of Ca and P (quadratic; P < 0.05) and increased ATTD of K and Na (linear; P < 0.05), but phytase did not influence the ATTD of Mg or gross energy. Concentrations of plasma P and bone ash increased (quadratic; P < 0.05), and plasma inositol also increased (linear; P < 0.05) with increasing inclusion of phytase. Reduced concentrations of inositol phosphate (IP)6 and IP5 (quadratic; P < 0.05), reduced IP4 and IP3 (linear; P < 0.05), but increased inositol concentrations (linear; P < 0.05) were observed in ileal digesta as dietary phytase increased. The ATTD of P was maximized if at least 1,200 FTU/kg were used, whereas more than 4,000 FTU/kg were needed to maximize inositol release. Increasing dietary levels of phytase after an 18-day adaptation period increased phytate and IP ester degradation and inositol release in the small intestine. Consequently, increasing dietary phytase resulted in improved digestibility of Ca, P, K, Na, and the first 4 limiting amino acids, and in increased concentrations of bone ash and plasma P and inositol. In a corn-soybean meal diet, maximum inositol release requires approximately 3,200 FTU/kg more phytase than that required for maximum P digestibility.