Effects of nutrient specifications and xylanase plus phytase supplementation of wheat-based diets on growth performance and carcass traits of broiler chicks

The simultaneous addition of xylanase (5,600 EXU/kg) and phytase (500 FTU/kg) feed enzymes to wheat-based broiler diets was investigated. Starter, grower and finisher diets, with three tiers of nutrient specifications, were fed to 1,440 broiler chicks kept on deep litter from 1-42 days post-hatch, without and with xylanase plus phytase, to determine the effects of diet type and enzyme supplementation on growth performance. The nutrient specifications of type A diets were standard; energy density and protein/amino acid levels were reduced on a least-cost basis to formulate type B diets and further reduced to type C diets. Phosphorus (P) and calcium (Ca) levels were adjusted in supplemented diets. From 1-42 days post-hatch, diet type significantly influenced growth performance. Birds on type C diets had lower growth rates (2,429 vs. 2,631 g/bird; p<0.001), higher feed intakes (4,753 vs. 4,534 g/bird; p<0.005) and less efficient feed conversion (1.96 vs. 1.72; p<0.001) than birds offered type A diets. Enzyme supplementation increased growth rates by 3.2% (2,580 vs. 2,501 g/bird; p<0.005) and improved feed efficiency by 2.7% (1.80 vs. 1.85; p<0.05) over the entire feeding period. There were no interactions between diet type and enzyme supplementation. At 21 days, 5 out of 30 birds per pen were transferred to cages to ascertain treatment effect on apparent metabolisable energy (AME) and nitrogen (N) retention. Xylanase plus phytase enhanced AME (13.48 to 13.91 MJ/kg DM; p<0.001) and N retention (56.3 to 59.7%; p<0.005). Carcass and breast weights of the caged birds were determined following commercial processing. Diet type significantly influenced breast weight, carcass weight and yield. Birds offered Type A diets, in comparison to Type C diets, supported heavier breast (467 vs. 424 g; p<0.001) and carcass weights (1,868 vs. 1,699 g; p<0.001) with superior carcass yields (71.8 vs. 70.6%; p<0.005). Enzyme addition increased carcass weight by 3.9% (1,752 vs. 1,821 g; p<0.005) and breast weight by 5.8% (431 vs. 456 g; p<0.01) without influencing yields. Feed ingredient costs per kg live weight gain and per kg carcass weight indicated that enzyme addition was economically feasible, where supplementation of Type A diets generated the most effective results. Importantly, soluble and total non-starch polysaccharide and phytate contents of the wheat used were typical by local standards. This study confirms the potential of supplementing wheat-based broiler diets with xylanase plus phytase but further investigations are required to define the most appropriate inclusion rates and dietary nutrient specifications in this context.