Impacts of phytase and coccidial vaccine on growth performance, nutrient digestibility, bone development, and intestinal gene expression of broilers fed a nutrient reduced diet

An experiment was conducted to evalu-ate effects of phytase and coccidial vaccine on growth performance, bone ash, bone 3-D microstructure, nutri-ent digestibility, and gene expression of intestinal bio-markers in broilers fed a regular or nutrient-reduced diet. The experiment was conducted in a 2 pound 4 factorial arrangement with 6 replicates per treatment and 10 birds per replicate. Two main factors were coccidial vaccine and dietary treatments. The dietary treat-ments included: 1) a positive control (PC; normal nutrient levels); 2) a negative control (NC; with a reduction of 0.15% of Ca and avP and 5% of essential amino acid (EAA) and crude protein relative to PC); 3) NC + 500 FTU/kg of phytase; and 4) NC + 1,500 FTU/kg of phytase. No interaction effect of phytase and coccidial vaccine on growth perfor-mance, bone ash, and apparent ileal digestibility (AID) was observed. For the main effect, birds fed the NC diet showed lower (P = 0.007) BWG during d 0 to 21 compared to PC birds, whereas supplementing 500 or 1,500 FTU/kg phytase increased BWG to the similar level to the PC. During d 0 to 21, vaccinated birds had a lower (P < 0.001) FI and better (P = 0.045) FCR compared to unvaccinated birds. Birds fed the NC diet resulted a decrease in tibia fat-free dry bone weight (P = 0.012), ash weight (P = 0.005), ash percentage (P < 0.001), and ash concentration (P = 0.019) com-pared to the PC group at d 21, whereas supplementing phytase at 500 or 1,500 FTU/kg in NC diet was able to improve these bone parameters to the similar level to the PC; however, vaccination did not have any effect on bone ash. Similarly, birds fed with the NC diet showed had significant lower bone microstructure levels including bone volume, bone mineral density, and bone mineral content (P < 0.001), and supplementing phy-tase at 1,500 FTU/kg improved these parameters. Vac-cination improved AID of nitrogen (P < 0.001). Birds from the NC and both phytase supplementation groups had a higher (P = 0.001) AID of Ca compared to the PC. Supplementing phytase at 500 FTU/kg or 1,500 FTU/kg improved (P < 0.001) AID of P com-pared to the NC. Additionally, the NC had a lower AID of DM than the PC, whereas supplementing phy-tase at 500 FTU/kg or 1,500 FTU/kg improved DM digestibility (P = 0.0299). In conclusion, supplementa-tion of phytase at 500 or 1,500 FTU/kg improved growth performance, bone mineralization, and nutrient digestibility regardless of vaccination, with a more pro-nounced effect when supplementing phytase at 1,500 FTU/kg.