Effect of different phytases on the performance, nutrient retention and tibia composition in broiler chickens

The effect of different phytases on the performance response, nutrient utilization and tibia characteristics of chickens was investigated. The five pelleted diets were the following: positive control (PC) with added monocalcium phosphate; negative control (NC) formulated with equivalency values of phytase for Ca and digestible P; and three further diets where different phytases were individually added to the NC diet at 500 FTU/kg. The phytases were derived either from Aspergillus (phytase I), or E. coli (phytases II and III). Compared to PC, the performance parameters, as well as apparent metabolizable energy (AMEn), mineral retention, bone breaking force and tibia mineral content were suppressed by the reduction of dietary Ca and digestible P. All phytases enhanced the overall body weight gains and feed conversion ratio in comparison with NC, but none outperformed PC. Only phytase II improved AMEn compared to NC and PC group. However only phytase I outperformed NC group in terms of mineral retention and P retention was higher than phytase II and III. No significant differences were observed in fat digestibility and N retention. Bone strength among phytases did not differ and all improved this parameter compared to the NC diet. However, even though all phytases enhanced tibia minerals content, the improvement was less pronounced with phytase III. Moreover, the differences in all analysed tibia minerals between phytase III and II were significant suggesting that even among 6-phytases derived from and expressed in the same organism, different efficacy or mode of action can occur.