Effects of phytase, calcium source, calcium concentration and particle size on broiler performance, nutrient digestibility and skeletal integrity

The study herein investigated the effect of mean particle size, calcium (Ca) source, Ca concentration and phytase on broiler performance, mineral digestibility and skeletal integrity from 1 to 28 days post-hatch. Sixteen dietary treatments were arranged in a 2 x 2 x 2 x 2 factorial design consisting of two Ca sources (limestone or a highly soluble calcium, HSC), two Ca concentrations (9.0 or 6.0 g/kg from Day 0 to Day 14 and 8.0 or 5.5 g/kg from Day 15 to Day 28), two Ca particle sizes (<0.5 or >0.5 mm) and two phytase-supplementation levels (0 or 1000 FTU/kg). Overall performance (Days 1-28) showed that the addition of phytase to diets containing 8.0 g/kg total Ca provided by HSC improved feed intake (P < 0.05), but there was no effect of the addition of phytase to birds fed Ca from limestone. Phytase supplementation decreased feed intake in birds fed limestone with a mean particle size >0.5 mm and increased feed intake in birds fed HSC with a mean particle size >0.5 mm, which resulted in a Ca source x Ca particle size x phytase interaction (P < 0.05). Birds fed diets containingHSChad a lower liveweight gain than did birds fed diets containing limestone (P = 0.03). Increasing the dietary Ca concentration from 5.5 g/kg to 8.0 g/kg total Ca decreased liveweight gain (P = 0.01). Phytase supplementation increased final liveweight gain (P<0.001). Foot ash was observed to be higher in birds that received diets containing 8.0 g/kg Ca (P < 0.05). Phytase supplementation increased foot ash percentage (P < 0.05). Phytase increased Ca digestibility in birds fed diets containing Ca provided by HSC with a mean particle size <0.5 mm and diets containing limestone with a mean particle size >0.5 mm (P < 0.05). Phytase increased Ca digestibility in birds fed 5.5 g/kg Ca, but had no effect on Ca digestibility in birds fed 8.0 g/kg Ca (P < 0.05). The addition of phytase to diets improved the digestibility of phosphorus, especially in birds fed diets containing limestone (P < 0.05), or 8.0 g/kg total Ca (P < 0.05), or diets with a mean particle size >0.5 mm (P < 0.05). The results of the present study are consistent with those of previous studies by the authors, which have shown that low dietary Ca in conjunction with phytase improves broiler performance and mineral digestibility. Phytase improved growth performance, regardless of Ca source or Ca concentration and improved mineral digestibility.