The objective of this study was to evaluate diets containing increasing levels of phytase (253, 759, 1265 and 1748 PU/kg of diets), by mean of bioavailability and minimum endogenous P losses. Twenty crossbred barrow weighting 32.19+2.17 kg were used in a randomized block design experiment, with five treatments and four replicates. The animals were kept in metabolic cages for a ten-day adaptation period and seven days for total collection of feces and urine. Blood samples were taken for seven days. At the first day of the collection period, each animal was injected intravenously with 7.4 MBq of 32P. At the end of the experimental period the animals were slaughtered and tissues of the muscle, heart, liver, kidneys and bones were collected for further studies. The levels of phytase enzyme did not affect the urinary P, retained P, plasma P and bioavailability, but a quadratic effect was observed for levels of phytase on P in feces and endogenous P. The minimum endogenous losses of P was more efficient than bioavailability to evaluate the effect of the phytase enzyme. The best utilization of the organic phosphorus occurs on the level 759 PU.
isotopic dilution; nonfat rice bran; phytase; swine; radiophosphorus
