L-Selenomethylselenocysteine Improves Growth Performance, Antioxidant Status, and Meat Quality in White-Feathered Broilers More Effectively than Selenomethionine

Selenium (Se) is essential in poultry nutrition for antioxidant defense through selenoproteins. While selenomethionine (Se-Met) is commonly used, L-selenomethylselenocysteine (L-SeMC) may offer more favorable responses for selected measured variables. This study compared Se-Met and L-SeMC effects on growth, antioxidant status, and meat quality in broilers. Six hundred and sixty one-day-old male Cobb 500 broiler chickens were randomly assigned to 11 dietary treatments, with six replicate pens of 10 birds per treatment, comprising a basal control diet and 10 selenium-supplemented diets arranged in a 2 × 5 factorial design (Se-Met or L-SeMC at 0.05, 0.10, 0.15, 0.20, or 0.25 mg Se/kg) for 42 days. Selenium supplementation significantly improved average daily gain, final body weight, and feed conversion ratio (p < 0.05). Model-estimated stationary points ranged from 0.137 to 0.142 mg/kg for Se-Met and 0.080–0.126 mg/kg for L-SeMC. Using source-specific model-estimated stationary points, L-SeMC showed 1.85- to 1.93-fold higher biological potency than Se-Met. Birds fed L-SeMC exhibited higher plasma glutathione peroxidase activity, lower malondialdehyde, improved meat color (higher a*_24h), higher ultimate pH, and lower drip loss (p < 0.05). L-SeMC is more effective than Se-Met for enhancing broiler growth, antioxidant capacity, and meat quality.