RESPONSE OF BROILERS TO GRADED-LEVELS OF MICROBIAL PHYTASE ADDED TO MAIZE-SOYBEAN-MEAL-BASED DIETS CONTAINING 3 LEVELS OF NON-PHYTATE PHOSPHORUS

Male 1-d-old broilers (n 920) were given 0, 200, 400, 600, 800, 1000 a nd 1200 U microbial phytase/kg diet in combination with 2.0, 2.7 or 3. 4 g non-phytate P (nP)/kg or 4.0, 5.1 or 5.8 g total P (tP)/kg in a 21 d trial to assess the effectiveness of phytase ina maize-soyabean-mea l diet, In addition to the above twenty-one diets, a positive control P diet supplied 4.5 g nP/kg, 6.9 g tP/kg and 10 g Ca/kg. The basal die t contained 230 g crude protein/kg, 8.8 g Ca/kg, 4.4 g tP/kg and 2.0 g nP/kg. Defluorinated phosphate and limestone were used to supply P an d Ca, A Ca:tP ratio of 2:1 was maintained except in the positive contr ol diet which had a ratio of 145:1. Phytase additions linearly increas ed (P < 0.01) body-weight (BW) gain, feed intake, toe ash percentage, and apparent retention (% of intake) or total amount (g/bird) of retai ned Ca and P, and Linearly decreased (P < 0.01) P excretion (g/kg of D M intake) at each level of nP with the magnitude of the response inver sely related to the level of nP. Above-normal mortality was only obser ved in the group receiving 2.0 g nP/kg diet without phytase, Adding nP linearly increased (P < 0.01) BW gain, feed intake, toe ash percentag e, Ca retention, total amount (g/bird) of P retained, and P excretion, and linearly decreased (P < 0.01) apparent retention (%) of P, Derive d linear and non-linear equations for BW gain and toe ash percentage a t the two lower nP levels, 2.0 and 2.7 g/kg, were used to calculate P equivalency values of microbial phytase, The results show that 939 U m icrobial phytase is equivalent to 1 g P from defluorinated phosphate i n broilers fed on maize-soyabean-meal diets, The amount of P released per 100 U phytase decreased as the total amount of phytase increased.