Efficacy of a novel phytase in response to low and high phytate diets using a short-term digestibility model in broiler chickens at two ages

A total of 2000 male broilers were used to evaluate the efficacy of a novel phytase in terms of phytate hydrolysis and apparent ileal digestibility coefficient (AIDC) of phosphorus (P) and calcium (Ca), in response to low and high phytate diets, using a short-term digestibility model in broiler chickens at two ages. The experimental diets were in a 2 x 5 factorial arrangement with 2 dietary phytate concentrations (low or high) and 5 doses of a novel phytase supplemented at 0, 500, 1000, 2000 FYT/kg or extradose (3000 or 4000 FYT/kg for low or high phytate diet, respectively). The extradosing of phytase was intended for nearly complete phytate hydrolysis when considering the phytate levels in the diet. Ten treatments with 10 replicate cages each were fed to birds for 36-hours at 9-11 or 19-21 days of age (12 or 8 birds per replicate). From day 9-11, a lower dose of phytase was able to improve feed conversion ratio (FCR) for birds fed high phytate diet, resulting in a phytase x phytate interaction (P < 0.05). Phytase supplementation (P < 0.05) or high phytate diet (P < 0.05) improved FCR at day 19-21, and increased body weight gain (BWG) at both ages. From day 9-11, a higher dose of phytase was required in birds fed high phytate diet to increase ileal phytate P degradation and AIDC of P comparable to the values of birds fed low phytate diet (phytase x phytate interaction, P < 0.05); whereas this interaction was not detected for birds at day 19-21, the two aforementioned measurements were increased with phytase supplementation (P < 0.05) or decreased with high phytate diet (P < 0.05). Interestingly, a phytase x phytate interaction (P < 0.05) was observed for AIDC of Ca, digestible Ca and P at both ages: a lower dose of phytase was needed to maximize AIDC of Ca and digestible Ca in high phytate diet when compared to low phytate diet; while a higher dose of phytase provided digestible P to a greater extent in high phytate diet compared with low phytate diet. In conclusion, phytase effectively hydrolyzed phytate P and increased digestible P and Ca. The impact of dietary phytate on phytase efficacy varied in terms of Ca or P response, and the extent of impact was different in younger compared with older birds.