Effect of dietary calcium concentration and exogenous phytase on inositol phosphate degradation, mineral digestibility, and gut microbiota in growing pigs

Variation in dietary Ca concentration may affect inositol phosphate (InsP) degradation and thereby P digestibility in pigs. The present study assessed effects of dietary Ca concentration and exogenous phytase on InsP degradation, nutrient digestion and retention, blood metabolites, and microbiota composition of ileal-cannulated growing pigs. In a completely randomized row column design with 4 periods, 8 ileal-cannulated barrows (initial bodyweight 27 kg) were fed 4 corn-soybean-and rapeseed meal-based diets containing 5.5 or 8.5 g Ca/kg dry matter (DM) without or with 1,500 FTU of an exogenous hybrid-6-phytase/kg diet. No mineral P was added, and the P concentration was 4.8 g P/kg DM. The prececal InsP6 disappearance in pigs fed diets with exogenous phytase was lower (P = 0.022) with additional Ca. Concentrations of InsP2-4 isomers and myo-inositol in distal ileum digesta and prececal P digestibility were greater (P < 0.001) with exogenous phytase compared to without exogenous phytase. In feces, InsP6 disappearance was lower (P < 0.002) and concentration of InsP5 and InsP4 isomers was greater (P = 0.031) with additional Ca compared to without additional Ca. The prececal amino acid digestibility, energy digestibility and hindgut disappearance of energy were not significantly different. Shannon diversity index of the microbiota in distal ileum digesta and feces did not differ among the diets but was lower in the distal ileum digesta than feces (P < 0.001). The permutation analysis of variance revealed no differences between bacterial community associated with diets within ileal digesta and fecal samples (P > 0.05). In conclusion, additional Ca reduced the exogenous phytase effect on prececal InsP6 degradation. Endogenous InsP degradation was impaired by additional Ca only in the hindgut, which may be related to the greater microbial diversity in feces compared to ileal digesta.