Effect of dietary calcium source, exogenous phytase, and formic acid on inositol phosphate degradation, mineral and amino acid digestibility, and microbiota in growing pigs

The choice of the Ca source in a pig diet and the addition of formic acid may affect the gastrointestinal inositol phosphate (InsP) degradation and thereby, P digestibility in pigs. This study assessed the effects of different Ca sources (Ca carbonate vs. Ca formate), exogenous phytase, and chemical acidification on InsP degradation, nutrient digestion and retention, blood metabolites, and microbiota composition in growing pigs. In a randomized row-column design with five periods, eight ileal-cannulated barrows (initial body weight 24 kg) were fed five diets containing Ca formate or Ca carbonate as the only mineral Ca addition, with or without 1,500 FTU/kg of an exogenous 6-phytase. A fifth diet was composed of Ca carbonate with phytase but with 8 g formic acid/kg diet. No mineral P was added, and the P concentration was 4.8 g P/kg dry matter (DM). Prececal InsP6 disappearance and P digestibility was lower (P = 0.032) in pigs fed diets containing Ca formate. In the presence of exogenous phytase, InsP5 and InsP4 concentrations in the ileal digesta were lower (P=0.019) with Ca carbonate compared to Ca formate. The addition of formic acid to Ca carbonate with phytase diet resulted in greater (P = 0.027) prececal InsP6 disappearance (87 vs 80%), lower (P = 0.001) InsP5 concentration and greater (P = 0.031) InsP2 and myo-inositol concentrations in the distal ileal digesta. Prececal P digestibility was greater (P = 0.004) with the addition of formic acid compared to Ca carbonate with phytase alone. Prececal AA digestibility of some AA was greater with Ca formate compared to Ca carbonate but only in diets with phytase (P = 0.048). The addition of formic acid to the diet with Ca carbonate and phytase increased (P = 0.006) the prececal AA digestibility of most indispensable AA. Exogenous phytase had an effect on the microbial community in the fecal samples and more genera were affected by phytase when Ca formate was used compared to Ca carbonate. In the ileal digesta samples, the Ca carbonate diet supplemented with formic acid and phytase led to similar microbial community than the Ca formate diets. In conclusion, Ca formate reduced prececal InsP6 degradation and P digestibility, but might be of advantage in regard to prececal AA digestibility in pigs compared to Ca carbonate when exogenous phytase is added to the feed. The addition of formic acid to Ca carbonate with phytase, however, resulted in greater InsP6 disappearance, P and AA digestibility values, and changed ileal microbiota composition compared to Ca carbonate with phytase alone.