ABSTRACT
This study was conducted to determine the effects of residual superdoses of phytase on growth performance, tibia mineralization, and relative organ weight in ducks fed phosphorus-deficient diets. In Exp. 1, 4 kinds of commercial phytase were used to determine retention rate of phyatse with the phytase C being the highest via both high water-bath temperature (90%) and pelleting (50%), followed by phytase A, B, and D. In Exp. 2, a total of 560 male ducks were blocked based on body weight, and then allocated randomly to 7 treatments (5 replicates with 16 birds per replicate). Treatments included a maize-soybean meal-based diet with recommended calcium and 4.0 g non-phytate phosphorus (nPP)/kg starter diet or 3.8 g nPP/kg grower diet (positive control; PC), an nPP-deficient diet with 1.3 g nPP/kg starter diet or 1.1 g nPP/kg grower diet (negative control; NC), NC diets with increasing levels of residual phytase C (500, 1,000, 2,000, 3,000, and 4,000 units/kg feed) after pelleting. Birds fed NC diets had lower (P < 0.05) average daily gain (ADG) and average daily feed intake (ADFI) throughout the experiment compared with those fed PC diet. Supplementing NC diet with increasing residual superdoses of phytase improved (P < 0.05) ADG and ADFI quadratically in the entire experiment, while reduced feed-to-gain ratio (P < 0.05) quadratically during day 0 to 14. On day 14 and 35, birds fed NC diet had lower (P < 0.05) tibia length, weight, ash, calcium, phosphorus, and manganese contents than those fed PC diet. Increasing residual superdoses of phytase in NC diet increased (P < 0.05) tibia weight and ash, calcium, phosphorus contents quadratically on day 14 and 35. NC treatment increased (P < 0.05) the duodenum, jejunum, ileum, and cecum index compared with other treatments on day 14 and 35. Taken together, feeding increasing residual superdoses of phytase could counteract or exceed the negative effects of NC diet on growth performance, tibia mineralization, and relative organ weight in ducks.
