The impact of estimation methods on phytase phosphorus equivalency for commercial layer hens

Abstract

An experiment was performed for evaluating calibration curve (CC) and comparing negative and positive controls (CNP) as a major method for estimating of phytase phosphorus equivalence for layer hens. Three hundred sixty 70-wk-old layer hens (W-36Hy-line) were used in a complete randomized design. Evaluated methods were setting the two regression equations for NPP-supplemented and phytase supplemented treatments with two sub-methods, include calibration curve (CC) or exclude phosphorus content of the basal diet (CC-BD) in calculation, and exploring enzyme equivalency by comparing phosphorus deficient diet as a negative and supplemented diet by inorganic phosphorus sources as a positive control group (CNP). Experiment included nine treatments (a phosphorus deficient basal diet contained 0.12% Av. P and 200, 300, 400 and 500 FTU/kg phytase was added to the basal diet, the rest four treatments were included basal diet supplemented with 0.20, 0.27, 0.35 and 0.43% Av. P). Each treatment in the experiment replicated five times, eight birds in each. Results indicated that methods of estimation had a significant effect on phosphorus equivalence estimation (p <0.0001). Fitted regression equations excluding P content of basal diet (CC-BD) estimated rational values than those ignore it (CC) (0.432% vs 0.564% for 500 FTU/kg phytase for layer hens) (p <0.0001). On average, among three methods used, CC method had the highest estimated values (p <0.0001). Regardless of mathematical method, there were no significant differences for egg production performance and egg quality traits served as response criteria (P˃0.05). In conclusion, the phosphorus equivalent value of enzyme varies according to the estimation methods. Hence, using matrix values of enzymes for accurate feed formulation depend on a variety of circumstances and decision making requires comprehensive information.