Effects of dietary Ca/P ratio, P level and microbial phytase supplementation on nutrient digestibilities in growing pigs: breakdown of phytic acid, partition of P and phytase activity along the intestinal tract

Light female pigs (26-61 kg) provided with a simple T-cannula about 10 cm p roximal to the ileo-caecal valve, were used in two experiments to investiga te 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 a ctivity along the alimentary tract in pigs. In experiment 1, two Ca/P ratio s (1.5/1 and 2.2/1) and two P levels (0.34 and 0.47%) were tested according to a 2 x 2 factorial arrangement within a Latin square design. In experime nt 2, the maize-tapioca-soybean meal-based diets of experiment 1 were suppl emented with phytase (500 FTU/kg). No lower inositolphosphates, but substan tial phytase activities were detected in the ileal digesta and faeces. Sign ificant faecal amounts of IP6 were found only for diets with a wide Ca/P ra tio, due to its antagonistic effect on phytase activity. The addition of fe ed phosphate increased the proportion of inorganic P (Pi), but reduced the phytase activity in the small intestine. Breakdown of IP6 at the terminal i leum was 16.2% for the diets without phytase supplementation and was due to microbial activity. Supplementation with phytase tripled the pre-caecal br eakdown 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 (SEY NAEVE et al.; J. Anim. Physiol. a. Anim. Nutr 83, 36-48, 2000), increased p hytase activity (+28%), higher organic nonphytate P fraction (+36%) and hig her amounts of bacterial residues or intestinal cell debris residues (+43%) in the small intestine. The digestibility experiments indicate that P abso rption from feed phosphate takes place to a large extent proximally to the ileo-caecal valve. The phosphorus that is liberated by added microbial phyt ase from phytate in feedstuffs causes an increase in the microbial populati on in the small intestine of pigs but only becomes available for absorption by the pig in the caecum/colon region.