Effects of dietary Ca/P ratio, P level and microbial phytase supplementation on nutrient digestibilities in growing pigs: precaecal, post‐ileal and total tract disappearances of OM,

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Abstract
Eight female pigs (26–61 kg) provided with a simple T‐cannula about 10 cm proximal to the ileo‐caecal valve, were used in two experiments to investigate the effects of Ca/P ratio, P level and supplementation with phytase (500 FTU/kg) on precaecal, post‐ileal and total tract disappearances of organic matter (OM), phosphorus (P) and calcium (Ca). In experiment 1, two Ca/P ratios and two P levels were tested according to a 2 × 2 factorial arrangement within a Latin square design. In experiment 2, the diets of experiment 1 were supplemented with phytase (500 FTU/kg). There was a substantial absorption of OM, P and Ca in the post‐ileal tract for all diets. Precaecal and total tract disappearances of OM were reduced by phytase addition (−4.4 and −0.8%, respectively). Supplementation with phytase resulted in an improvement of total tract and post‐ileal P disappearances by 10.3 and 12.1%, respectively, without affecting precaecal P disappearance. Addition of feed phosphate resulted in a higher precaecal disappearance of P (+10.8%), resulting in a higher total tract disappearance of P (+5.9%). Addition of limestone had little effect on disappearances of OM, P and Ca, but reduced activity of supplemental phytase and had a negative influence on growth performance. Precaecal, post‐ileal and total tract Ca disappearances were hardly affected by the examined dietary factors. The results might indicate that P from feed phosphate is absorbed primarily prececally and that P from phytate, liberated by microbial phytases, is dominantly absorbed post‐illeally.

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