Reevaluating manganese requirements of broiler chickens under phytase supplementation.

Manganese (Mn) is routinely supplemented in broiler diets to prevent deficiency and sustain optimal performance, while phytase is known to enhance trace mineral availability in corn-SBM feeds. This study evaluated graded Mn supplementation in diets with or without phytase. A total of 640 one-day-old male Cobb × Cobb 500 chicks were assigned to a 2 × 5 factorial design (with or without phytase × five Mn levels). Birds were housed in 80 battery cages, with 8 replicates of 8 birds each. From placement to 7 days, all chicks received a Mn-deficient diet without phytase (14.58 ± 0.74 mg/kg analyzed Mn). From 7 to 28 days, corn-SBM diets (19.64 ± 1.5 mg/kg analyzed Mn) were fed with phytase at 4,000 FYT/kg (analyzed 4,680 ± 420 FYT/kg) and Mn, supplied as MnSO₄·H₂O, to achieve 19.64 ± 1.5, 44.08 ± 0.67, 73.80 ± 1.26, 105.08 ± 2.76, and 129.97 ± 1.59 mg/kg analyzed Mn. No interactions between phytase and Mn were detected (P > 0.05). Phytase significantly improved growth performance, dry matter and Mn retention (P < 0.001), and AMEn (P < 0.05). Increasing dietary Mn had no effect on growth performance, locomotor parameters, or tibia morphometry at 28 days (P > 0.05), whereas Mn excretion and retention increased linearly with higher dietary inclusion (P < 0.001). Tissue Mn concentrations in tibia and liver, as well as heart Mn superoxide dismutase (Mn-SOD) activity, responded quadratically, with estimated maxima at 124.2, 180.6, and 105.8 mg/kg Mn, respectively (P < 0.05). These results indicate that current Mn supplementation practices in commercial broiler feeds may exceed requirements when growth performance is the primary response criterion. Improvements associated with phytase are consistent with previous findings for other trace minerals. However, Mn-SOD responses suggest that dietary Mn levels required to support antioxidant defense and mitigate oxidative stress may be higher than those needed to optimize conventional performance metrics.