Microbial phytase in finisher diets of White Pekin ducks: Effect on growthperformance, plasma phosphorus concentration, and leg bone characteristics

Two experiments (Exp,) were conducted to determine the growth response of W hite Pekin ducks to inclusion of microbial phytase in finisher diet. In Exp . 1, 1-d-old male ducks (240 total) were reared in litter-floor pens and fe d regular starter diet until 3 wk of age. At 3 wk Of age, ducks were random ly divided into six groups of 10 ducks each and each group was fed one of f our diets. Three finisher diets containing 16% CP and 0.18% available phosp horus (AP) without supplemental P were formulated with microbial phytase (N atuphos(R)) added at 0, 750, or 1,500 phytase units/kg of diet. The fourth diet was a control finisher diet that was supplemented with dicalcium phosp hate (DCP) to supply dietary AP of 0.41%, Group BW and feed intake were mea sured weekly to assess growth response. At 6 wk of age, leg bones (tibia, f emur, metatarsus) from five randomly selected ducks were removed and analyz ed for bone characteristics. In Exp. 2, a total of 120 ducks reared as in E xp. 1 were randomly divided into six groups of five ducks each and fed one of four diets. A basal finisher diet was formulated to contain 16% CP and 0 .18% AP. Monosodium phosphate was added to the basal diet to give dietary A P levels of 0.18, 0.27, and 0.36%. The fourth diet was the basal diet suppl emented with microbial phytase (750 phytase units/kg of diet). Ducks were f ed these diets from 3 to 6 wk of age. At the end of the study, ducks were b led by cardiac puncture and blood plasma was analyzed for P concentration. Leg bones from all ducks were removed and analyzed for bone characteristics as in Exp. 1. Feed intake increased linearly with increased level of dieta ry phytase, whereas the weight gain response was quadratic only during the last week of Exp. 1. Ln Exp. 2, there was a quadratic response for weight g ain due to dietary AP. Weight gain due to phytase (750 units) was not diffe rent from ducks fed diets at 0 or 0.18% AP. Plasma P concentration increase d linearly as dietary AP increased. Plasma P levels of ducks fed phytase we re similar to those of ducks fed 0.18% AP but lower than in ducks fed 0.27% AP. Estimates of AP resulting from the addition of 750 units of phytase to basal diet were 0.05 and 0.07% based on plasma P concentration and weight gain, respectively. Using regression analysis, the AP due to phytase effect in the diet was estimated to range from 0.06 to 0.08%. Results suggest tha t phytase can be used in finisher diets similar to the one used in this stu dy for ducks from 3 to 6 wk of age to improve growth performance and leg bo ne development similar to ducks fed diets supplemented with P from inorgani c sources.