Abstract:
Phytases are supplemented to poultry diets to hydrolyse phytate, improve digestibility of P and thereby decrease P excretion and feed cost. It has been shown that the in vivo efficacy can differ between phytase sources, leading to differences in the slope and asymptote in the response in digestible P with increasing phytase dose. The objective of this study was to compare the effect of different statistical methods and sampling criterion on the efficacy of three phytase enzymes in young broiler diets on performance parameters (body weight (BW), body weight gain (BWG) and FCR) as well as bone mineralisation. A mash corn-soy based negative control diet was supplemented with each phytase product based on analysed phytase units (FTU) at the five dose levels (500, 1000, 1800, 2500 and 3500 FTU/kg) to form a dose response which was compared against three positive control (PC) diets that contained incremental amounts of monodicalcium phosphate. BW, BWG and FCRm were determined from 4-14 days. On day 14, eight broilers/cage were sampled, the right tibia removed, pooled by cage, and defatted tibia bone ash weight and content were determined. Bone ash, BW, BWG and FCRm were plotted against analysed phytase dose to compare the slope and asymptote parameter estimates in the nonlinear equation: y=a+b*cx. The results from this study suggest large differences in the in-vivo efficacy of newly developed phytases based on differences in the gradient and asymptote of the response in bone ash, BW, and FCRm.
