The impact of dietary calcium content on phosphorus absorption and retention in growing pigs is enhanced by dietary microbial phytase supplementation

Sixty growing male pigs were used to test the hypothesis that high dietary Ca content reduces P absorption to a greater extent in microbial phytase-supplemented diets via reducing inositol phosphate (IP) degradation and enhancing P precipitation. Pigs were equally allotted over diets with three Ca contents 2.0, 5.8 and 9.6 g/kg with or without microbial phytase (0 vs. 500 FTU/kg) in a 2×3 factorial arrangement. Faeces and urine were collected at the end of the 21-day experimental period. Subsequently, pigs were euthanized and digesta quantitatively collected from different gastrointestinal tract (GIT) segments. Increasing dietary Ca content reduced apparent P digestibility in all GIT segments posterior to the stomach (P<0.001), with greater effect in phytase-supplemented diets in the distal small intestine (P interaction=0.007) and total tract (P interaction=0.023). Nonetheless, increasing dietary Ca to 5.8 g/kg enhanced P retention, but only in phytase supplemented diets. Ileal IP6 degradation increased with phytase (P<0.001) but decreased with increasing dietary Ca content (P=0.014). Proportion of IP esters in total IP (ΣIP) indicated that IP6/ΣIP was increased while IP4/ΣIP and IP3/ΣIP were reduced with increasing dietary Ca content, also with a greater impact in phytase-supplemented diets (P interaction=0.025, 0.018 and 0.009, respectively). In all GIT segments, P solubility was increased with phytase (P<0.001) and tended to be reduced with dietary Ca content (P