Does estimation methods affect on phosphorus equivalence value of phytase for layers and broiler chickens?

Abstract

Two experiments were 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 and broiler chickens. In the first and second experiments, 360 Hy-line W-36 layer hens and 525 day-old Ross-308 broiler chickens were used in a complete randomized design, respectively. 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 the amount of phosphorus content of basal diet (CC-BD) in calculation, and exploring enzyme equivalency by comparing phosphorus deficient diet as an negative and supplemented diet by inorganic phosphorus sources as a positive control group (CNP). Experiment one included nine treatments (200, 300, 400 and 500 FTU/kg phytase was added to a phosphorus deficient basal diet contained 0.12% Av.P, the rest four treatments were included basal diet supplemented with 0.20, 0.27, 0.35 and 0.43% Av.P). Experiment two included seven treatments (a basal P deficient diet contained 0.27% Av.P, and two increasing levels of Av.P, 0.32 and 0.37%, and four doses of phytase 200, 300, 400 and 500 FTU/kg added to basal diet). Each treatment in the both experiments replicated five times. Results indicated that methods of estimation had a significant effect on phosphorus equivalence estimation (P<0.0001). Fitted regression equations considering P content of basal diet (CC-BD) estimated rational values than those ignore it (CC) (0.161% vs 0.424% and 0.432% vs 0.564% for 500 FTU/kg phytase for broiler chicken and layer hens, respectively) (P<0.0001). On average, among three methods used, CC method had the highest estimated values both in broiler chickens and layer hens (p<0.0001). Regardless of mathematical method, there were different significant values for different strains (layer, 0.381% and broiler, 0.212%) (P<0.0001), but not for different traits served as response criteria (P>0.05). In conclusion, the phosphorus equivalent value of enzyme varies according to the estimation methods and strain. Hence, using matrix values of enzyme for accurate feed formulation depend on a variety of circumstances and decision making requires comprehensive information.