Effect of microbial phytase on apparent digestibility and retention of phosphorus and nitrogen in growing pigs

Six female pigs of approximately 50 kg BW, fitted with simple T-cannula in the terminal ileum, were used to study the effect of microbial phytase on apparent total tract digestibility and retention of P and N. Three P-adequate diets (digestible P concentration 2.3 g/kg) containing barley (B), soybean meal (S) or their mixture (BS) with or without phytase supplement (1000 FTU/kg) were fed to pigs using a 6 x 6 Latin square design. The addition of phytase increased (P < 0.05) apparent total P digestibility of diets S and BS from 56.5 and 57.2% to 69.0 and 65.2%, respectively, and apparent plant P digestibility of the same diets from 41.3 and 50.0% to 60.5 and 60.0%, respectively. An insignificant improvement in total and plant P digestibilities was found in diet B. Phytase supplementation reduced (P < 0.05) P excretion in pigs fed diets S and BS by 25 and 14%, respectively. As compared with diets S and BS, urinary P excretion in pigs fed diet B was much higher, which suggests a lower requirement for available P due to the lower protein deposition and growth rate. Phytase supplementation had no effect on digestibility or retention of N. In all three diets, total tract P digestibility was lower (P < 0.05) than ileal digestibility thus indicating a net flux of P into the large intestine.