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

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.