The objective of this study was to determine the optimal dose of the new generation modified E.coli 6-phytase (modified E.coli) that was developed using gene site saturation mutagenesis, and to compare its efficacy to current heat-stable phytases under typical South African commercial broiler production conditions. A total of 2,340 as-hatched Cobb 500 chicks were randomly allocated to nine treatment groups, each replicated 13 times with 20 chicks per pen. The first three treatments consisted of two negative control diets and a positive control diet as follows: negative control (NC1) – starter diet with 0.23% available phosphorus (avP); NC2 – starter diet with 0.33% avP; positive control (PC) – starter diet with 0.43% avP. For each control, the finisher diets had a 0.11% reduction in avP. The remaining six treatments consisted of NC1 supplemented with three different phytase products (modified E.coli, product X and product Y) at two different doses for each product (500 FTU/kg diet and 1,000 FTU/kg diet). Production performance parameters, bone strength, bone ash content and bone mineral content were evaluated.
Broilers fed the NC1 diet showed a significantly lower (P<0.05) body weight, feed conversion ratio (FCR), production efficiency factor (PEF), bone strength and ash compared to all other treatment diets. All phytase-supplemented treatments showed results similar to the PC diet (P>0.05). No significant differences were detected among phytase-supplemented treatments. Numerically (P>0.05), broilers fed the diet supplemented with modified E.coli at 500FTU/kg had the greatest body weight, cumulative feed intake and PEF values, and the lowest FCR values on day 35 compared to all other phytase-supplemented diets. Numerically, in terms of bone development broilers fed a diet containing phytase at 1,000FTU/kg had the highest bone breaking strength compared to their 500FTU/kg counterparts, with modified E.coli numerically scoring the highest bone breaking strength, ash and phosphorous deposition, followed by product X and then product Y. In conclusion, broiler performance using this new generation modified E.coli 6-phytase product is comparable to other phytase products on the South African market at an optimal dose of 500FTU/kg diet.