The effects ofmicrobial phytases and dietary calcium and phosphorus levels on the productive performance and bone mineralization of broilers

Two trials were conducted to evaluate the effects of phytase and different levels of calcium (Ca) in an available phosphorus-limited diet (aP) on the performance, bone mineralization, and Ca and P retention of broilers. In Trial 1, 160 one-day-old male broilers were placed into 40 cages and allocated to five dietary treatments: one positive control [PC, 4.7 and 4.3 g/kg non-phytate P (NPP) and 9.0 and 8.5 g/kg Ca, from 1 to 21 days (d) and from 21 to 35 d of age, respectively] and four negative control [NC, 3.2 and 2.9 g/kg NPP and 7.0 and 6.3 g/kg Ca in starter (1-21 d) and growth (22-35 d) diet] groups comprising 4 concentrations of phytase A (FLF® 1000 FUT, 0, 250, 500 and 1000 FTU/kg). In Trial 2, 300 one-day-old broilers were placed into 60 cages and allocated to 10 dietary treatments, consisting of two NC diets (3.2 g/kg NPP), either 7.0 g/kg Ca (low Ca) or 9.0 g/kg Ca (high Ca), supplemented (0 or 500 FTU/kg) with four different phytases [OptiPhos® 5000 CT (A), Phyzyme® XP10000 TPT (B), Ronozyme® NP (C) and FLF® 1000 FUT (D)] from 1 to 14 d. In Trial 1, the PC group and the group receiving the highest dose of phytase A FLF® 1000 FUT (1000 FTU/kg) yielded significantly higher average daily gains from 1 to 21 d and higher tibia weights and ash contents than the NC, 250, and 500 FTU/kg. In Trial 2, no differences were observed in performances between animals receiving different types of phytase. Low Ca diets improved the feed efficiency from 1 to 7 d and ileal P digestibility. The interaction between Ca:aP and phytase affected (P ≤ 0.05) the feed efficiency from 1 to 7 d and ADG from 7 to 14 d. Based on this study, high levels of phytase (1000 FTU/kg) supplemented in starter (1-21 d) and growth (22-35 d) diets containing 3.2 and 2.9 g/kg NPP and 7.0 and 6.3 g/kg Ca, respectively, may be required to promote performance and bone mineralization in growing broilers. Lowering Ca levels to 7 g/kg in starting diets may exert greater effects on performance and ileal P digestibility than low levels (500 FTU/kg) of phytase.