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

An experiment was performed to evaluate the calibration curve (CC) and compare the negative and positive controls (CNP) as a major method for estimating the phytase phosphorus equivalencies for layer hens. Three hundred and sixty 70-wk-old layer hens (W-36Hy-line) were used in a completely randomized design. Evaluated methods were setting two regression equations for NPP-supplemented and phytase supplemented treatments with two sub- methods by including the calibration curve (CC) or excluding the phosphorus content of the basal diet (CC-BD) in calculations, 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). The experiment included nine treatments (a phosphorus deficient basal diet containing 0.12% available phosphorus (Av. P), 4 basal diets containing 200, 300, 400 and 500 FTU/kg phytase, and four basal diets supplemented with 0.20, 0.27, 0.35 and 0.43% Av. P). Each treatment was replicated five times with eight birds per replicate. Estimation method had a significant effect on phosphorus equivalency estimation (P 0.0001). Fitted regression equation models that deducted the P content of the basal diet (CC-BD) provided more rational values than those method ignore it (CC) (0.432% vs 0.564% for 500 FTU/kg phytase for layer hens) (P 0.0001). Of the three methods used, the CC method provided the highest estimated values (P 0.0001). Regardless of the mathematical methods, there were no significant differences for egg production performance and egg quality traits served as the response criteria. It was concluded that the phosphorus equivalent value of enzyme varied according to the estimation methods; therefore, using the matrix values of enzymes for accurate feed formulation depends on a variety of circumstances, and decision making requires comprehensive information.