Abstract
BACKGROUND AND AIM: Methionine is an essential amino acid in broiler nutrition, playing a crucial role in growth performance and liver metabolism. As an alternative to antibiotic growth promoters (AGPs), this study aimed to evaluate the effects of DL-Methionine and L-Methionine supplementation on liver metabolism, antioxidant activity, and growth performance in broilers raised without AGPs. MATERIALS AND METHODS: A total of 440 one-day-old Cobb 500 male broiler chicks were assigned to 11 groups: A control group and 10 treatment groups receiving graded levels (70%, 85%, 100%, 115%, and 130%) of either DL-Methionine or L-Methionine. The study assessed body weight, liver mass index, D-amino acid oxidase (DAAO) activity, serum glutathione concentration, and liver histopathology across three growth stages: Starter (day 11), grower (day 25), and finisher (day 35). RESULTS: L-Methionine supplementation resulted in greater body weight gain compared to DL-Methionine, particularly in the finisher stage. DL-Methionine demonstrated a stronger influence on liver metabolism by increasing DAAO activity and reducing oxidative stress, as indicated by lower serum glutathione levels. No significant histopathological alterations were observed among the groups, confirming the safety of both methionine sources. CONCLUSION: While L-Methionine improved growth performance, DL-Methionine effectively enhanced liver metabolism and reduced oxidative stress. These findings suggest that DL-Methionine may support liver function, whereas L-Methionine is more effective for weight gain in broilers raised without AGPs.