The effect of phytase source, wheatmiddlings, and citric acid on phosphorus utilization, growthperformance, andcarcass yield in broilers

A study was conducted to investigate the impact of phytase source, citric acid, and wheat middlings (WM) on growth performance, bone strength, carcass yield, and P release in broilers fed marginally-deficient P diets from d 21 to 55. The experiment consisted of 13 dietary treatments, which were replicated five times, where each replicate consisted of 20 birds and utilized the standard-curve methodology using monobasic potassium phosphate (KH ₂PO₄) as the standard. Treatments were as follows: diets 1 to 4) corn -soybean meal (C-SBM) basal (0.13% iP) supplemented with graded levels (0, 0.04, 0.08, 0.12%) of KH₂PO₄; diets 5 to 8) as in diet 1 with 500 FTU/kg of phytase (E. coli (EP) or fungal (FP)) and two levels of citric acid (0 or 3%); diet 9) as in diet 1 with 10% corn replaced by WM; and diets 10 to 13) as in diet 9 supplemented with 500 FTU/kg of phytase (EP or FP) and two levels of citric acid (0 or 3%). Reducing dietary IP had no impact on growth performance. Phytase had the main effect of increasing weight gain in the grower and withdrawal phases (P < 0.05); weight gain was greater in broilers fed the EP diets compared to those fed the FP diets during the grower phase (P < 0.05). When all the periods were combined only broilers fed the EP diets had weight gains and feed efficiencies that were greater than broilers fed no supplemental phytase (P < 0.05). The inclusion of phytase had the main effect of increasing adjusted bone breaking strength (ABBS) and tibia ash (P < 0.05) and released at least 0.083% P. Broilers fed the FP diets had lower carcass yield, whereas broilers fed the EP diets had lower wing yield (P < 0.05). Citric acid had the main effect of increasing feed efficiency, ABBS, and tibia ash (P < 0.05) when all the periods were combined. Phytase and citric acid released at least 0.100% P, whereas the inclusion of WM alone released 0.051% P using ABBS data. The combination of phytase and WM increased P release by 67% (P < 0.05), whereas phytase, citric acid, and WM released at least 0.148% P.