The net energy (NE) value may be a better measure than apparent metabolizable energy (ME) of the effect of supplemental
phytase on energy utilization in broilers. The present study was conducted to assess the impact of 3 microbial phytases supplemented at an unconventionally high level (1,000 FTU/kg feed) on performance and NE of broilers using the indirect calorimetric method (IC). Four treatments included: 1) Control, formulated to be deficient in ME (12.35 MJ/kg in the starter diet; 12.56 MJ/kg in the grower diet),
calcium (0.72% in the starter diet; 0.60% in the grower diet), and available
phosphorus (0.25% in the starter diet; 0.20% in the grower diet); 2) control + intrinsically thermostable
phytase A; 3) control + intrinsically thermostable
phytase B; and 4) control + coated
phytase C. A completely randomized design was employed. A total of 384 male broiler chicks were used, and each treatment had 6 replicates with 16 birds per replicate. The birds were reared until d 21 in floor pens with hardwood shavings. Thirty-two birds (8 birds per treatment) were randomly selected to determine heat production and NE (from 25-28 d) following a 3-d acclimatization in the respiratory chambers. Performance results at d 21 showed that supplementation with either of the 3 phytases improved
body weight (P < 0.001) and feed intake (P < 0.05), and increased the relative weights of tibia ash (P < 0.05) and
toe ash (P < 0.01). Phytases A and B increased the NE value of the diet (P < 0.05). It may be concluded that the negative effects imposed by
calcium and available
phosphorus down-specification can be compensated by
phytase supplementation in general, and intrinsically thermostable phytases improve the ME and NE value. However,
phytase did not reduce heat production, heat increment, or increase NE:ME in birds.