Research note: Evaluation of therapeutic copper levels on phytase efficacy in young broilers

The use of prophylactic levels of Cu at doses of 150-250 mg/kg, may be used in commercial broilers to achieve antimicrobial benefits. However, Cu interactions with phytic acid may impact mineral bioavailability and reduce phytase efficacy. This study assessed the effects of Cu source and dose on growth performance and bone mineralization in broilers when diets contained graded levels of phytase. The trial utilized a 3 × 6 factorial, incorporating three Cu treatments, copper sulfate (CuSO₄) at 10 and 200 mg/kg, and 200 mg/kg from monovalent copper (Cu₂O) and six doses of a novel synthetic 6-phytase per Cu treatment (0, 500, 1,000, 1800, 2,500 and 3,500 FTU/kg). The basal diet free of inorganic P was formulated with a low P, and Ca content (1.2 g/kg dP, 3.4 g/kg P and 0.70% Ca) to which Cu and phytase was added to make 18 treatments. Broiler BW was determined for the trial period (4-10 d). On d 10, broilers were sampled, and the right tibia was removed and pooled per pen to determine defatted tibia bone ash (%). Data were analyzed in JMP using the fit model platform to evaluate linear and quadratic responses to phytase, interactions with Cu, and non-linear regression for each Cu treatment. Broiler BW and tibia ash% showed significant (P < 0.05) linear and quadratic responses to increasing phytase doses. No Cu × phytase interaction was observed for BW, with similar asymptote, scale, and rate constant across Cu treatments. For tibia mineralization, a significant Cu source × phytase interaction was observed (P < 0.05). Diets supplemented with 200 mg/kg Cu₂O reached the asymptote in tibia ash % at a lower phytase dose compared to 200 mg/kg and 10 mg/kg CuSO₄ (P < 0.05). Nonlinear regression indicated that tibia ash achieved 95% of the asymptote at 1,550 FTU/kg phytase for CuSO₄ and 1,000 FTU/kg for Cu₂O, suggesting reduced susceptibility of Cu₂O to phytic acid chelation. These results indicate that Cu source and dose influence bone mineralization and phytase efficacy in young broilers.