Effect of betaine on growth performance, methionine metabolism, and methyl transfer in broilers aged 1 to 21 days and fed a low-methionine diet

Betaine has been proposed as a low-cost source of methyl groups in poultry feed, replacing methionine and choline. The present study aimed to investigate the effect of betaine on growth performance, methionine metabolism, and methyl transfer in broilers aged 1 to 21 days fed a low-methionine diet. A total of 960 one-day-old male broilers were randomly divided into four groups: positive control (0.62% methionine in the diet), negative control (0.37% methionine in the diet), and two treatment groups (0.37% methionine in the diet plus either 1500 or 3000 mg betaine/kg diet). Chicks fed the 1500 mg betaine/kg diet had the highest feed-to-gain ratio (P < 0.05), but no significant difference in final body weight, average daily gain, average daily feed intake, or mortality. Serum S-adenosyl-L-methionine and total homocysteine were higher at 1500 mg betaine/kg diet; whereas serum S-adenosylhomocysteine exhibited the opposite trend. Except for DNA methyltransferase 1, key enzymes and metabolites involved in the hepatic single-carbon pathway showed the highest levels at 1500 mg betaine/kg diet and declined thereafter. Furthermore, betaine promoted dose-dependent mRNA and protein expression of enzymes involved in the hepatic single-carbon metabolic cycle and methyl transferase pathways in chicks fed methionine-deficient diets. In conclusion, while the addition of betaine did not significantly improve the growth performance of chicks aged 1–21 days, inclusion of 1500 mg betaine/kg diet effectively stabilized methionine metabolism and methyl transfer in methionine-deficient diets.