Summary
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 the breakdown of phytic acid (IP6), partition of P and phytase activity along the alimentary tract in pigs. In experiment 1, two Ca/P ratios (1.5/1 and 2.2/1) and two P levels (0.34 and 0.47%) were tested according to a 2 × 2 factorial arrangement within a Latin square design. In experiment 2, the maize‐tapioca‐soybean meal‐based diets of experiment 1 were supplemented with phytase (500 FTU/kg). No lower inositolphosphates, but substantial phytase activities were detected in the ileal digesta and faeces. Significant faecal amounts of IP6 were found only for diets with a wide Ca/P ratio, due to its antagonistic effect on phytase activity. The addition of feed phosphate increased the proportion of inorganic P (Pi), but reduced the phytase activity in the small intestine. Breakdown of IP6 at the terminal ileum was 16.2% for the diets without phytase supplementation and was due to microbial activity. Supplementation with phytase tripled the pre‐caecal breakdown of IP6. However, the liberated Pi along the small intestine was not absorbed by the animal, but incorporated in microbial biomass as shown by lower organic matter (OM) disappearance and unaffected P disappearance ( Seynaeve et al.; J. Anim. Physiol. a. Anim. Nutr. 83, 36–48, 2000 ), increased phytase activity (+28%), higher organic nonphytate P fraction (+36%) and higher amounts of bacterial residues or intestinal cell debris residues (+43%) in the small intestine. The digestibility experiments indicate that P absorption from feed phosphate takes place to a large extent proximally to the ileo‐caecal valve. The phosphorus that is liberated by added microbial phytase from phytate in feedstuffs causes an increase in the microbial population in the small intestine of pigs but only becomes available for absorption by the pig in the caecum/colon region.
