ABSTRACT: The objective of the present experiment was to determine the efficacy and the phosphorus (P) equivalency of phytase in the corn-soybean meal-rapeseed meal diets of Cherry Valley ducks from 1 to 35 d of age. 320 ducks were randomly divided into 8 blocks of 5 cages with 8 ducks per cage. This experiment included eight treatments diets. The available P levels of I to IV treatments were respectively 0.25%, 0.32%, 0.39%, 0.46% (d 1-14) and 0.20%, 0.27%, 0.34%, 0.41% (d 15-35). And 4 levels of phytase added to low-P basal diet (treatment I) with 300, 600, 900, and 1,200 U/kg (treatment V to VIII). Among them, treatment IV was a P-adequate positive control, treatment I was a low-P negative control. The ratio of calcium (Ca) to P was 1.3:1 for all diets. The other nutritional indexes in all diets were basically the same. Ducks were provided ad libitum access to water and experimental diets. The negative control diet reduced (P < 0.05) body weight, carcase weight, eviscerated weigh, breast muscle weight, leg muscle weight, bone ash, tibia Ca and tibia P, and increasing levels of available P and supplementary phytase significantly (P < 0.05) improved the growth performance and slaughtering performance of meat ducks. Phytase supplementation at a dose of 900 U/kg in the low-P basal diet increased the growth performance of ducks to a level comparable to that of a P-adequate diet. The available P level of 0.39% (1-14 d) and 0.34% (15-35 d) could meet the nutritional needs of meat ducks for P, and the apparent P utilization rate was high, and the effective utilization effect of P was the best. In addition, with the evaluation indexes of feed intake, body weight gain, tibia ash, tibia Ca, tibia P, content of blood Ca and P, the addition of 500 U/kg phytase could release available P of 0.02%, 0.02%, 0.02%, 0.02%, 0.01%, 0.04%, and 0.03%, respectively. In the same way, the addition of 1,000 U/kg phytase could release available phosphorus of 0.14%, 0.04%, 0.04%, 0.05%, 0.02%, 0.12%, and 0.01%, respectively.
