Phytase effects on the efficiency of utilisation and blood concentrations of phosphorus and calcium in Pekin ducks.

1. The objective was to study the effects of a supplementation of a 6-phytase derived from the Peniophora lycii gene in the White Pekin duck. 2. In two balance studies, low-phosphorus (P) diets consisting mainly of maize, solvent extracted soybean meal and solvent extracted sunflower meal were supplemented with phytase up to concentrations of 1500 U/kg (Study 1) or 2000 U/kg (Study 2). Each diet (phytase level) was fed to 8 to 10 individually penned ducks. The intake and excretion of each animal was measured for 5 consecutive days when ducks were in their third week of life. Responses were described by nonlinear regression. 3. Although the basal diets from the two studies were similar in ingredient composition, efficiencies of P utilisation (P accretion/P intake x 100) for the unsupplemented basal diets were 39% in Study 1 and 30% in Study 2. Phytase supplementation significantly improved P utilisation up to levels of about 55% in both studies. A plateau in P utilisation with an increase in phytase supplementation was achieved in Study 2, but not in Study 1. The enzyme was more efficient in Study 2 than in Study 1 at low rates of supplementation. Utilisation of calcium (Ca) was significantly improved by phytase supplementation. Accretions of P and Ca increased at a constant ratio. 4. In a 5-week growth study, diets with an intentionally marginal P level were used. Diets were fed either unsupplemented or supplemented with 1000 or 10,000 U/kg of phytase. Eight pens of 10 sex-separated ducks each (4 pens per sex) were allocated to each dietary treatment. 5. Phytase significantly improved the growth of ducks of both sexes between d 1 and 21, but not between d 22 and 35. Feed conversion rate was not affected by treatment. Blood serum phosphate concentrations, but not calcium, were significantly increased by phytase supplementation. Blood concentrations of creatinine, aspartate aminotransferase and lactate dehydrogenase remained unaffected while alanine aminotransferase was significantly reduced by phytase supplementation. 6. It was concluded that the efficacy of a microbial phytase varies even under similar experimental conditions. Differences in intrinsic phytase activity of maize/soybean meal-based diets may be responsible for this. The 6-phytase used has the potential to improve the utilisation of plant P in duck feeding. A plateau in response was reached above 1500 U/kg.