Evaluation of the effects of microencapsulated DL-methionine on productive performance, immunity, plasma amino acids, and hepatic growth-related gene expression in broilers

Abstract

A 42-day feeding trial was conducted to compare a diet supplemented with crystalline DL-methionine (control) with diets containing microencapsulated DL-methionine (MEM) supplied at 60, 70, 80, 90, or 100 % of the commercially recommended level in broiler chickens. A total of 1260 one-day-old Arian broilers were randomly allotted to six treatments, with seven replicates of 30 birds each. Body weight gain (BWG), feed intake, and feed conversion ratio (FCR) did not differ between birds fed the control diet and those fed MEM diets containing ≥70 % of the recommended level, whereas the 60 % MEM diet reduced BWG and increased FCR. Increasing the dietary MEM level resulted in a quadratic increase in leg yield and a linear decrease in abdominal fat, without affecting hematological traits or leukocyte differential counts. The 100 % MEM diet increased influenza (H9N2) antibody titers, and all MEM levels enhanced Newcastle disease virus titers compared with the 60 % MEM diet; moreover, titers in the 100 % MEM group also exceeded those of the control. Plasma methionine, serine, and total amino acid concentrations were higher in birds fed the 60 % MEM diet than in those fed the 90 % MEM diet, while plasma cysteine showed a quadratic response as MEM level increased. Diets providing 80–100 % MEM upregulated hepatic GHR expression, and diets providing 90–100 % MEM also increased mTOR expression compared with the 60 % MEM diet. Overall, microencapsulated DL-methionine enabled approximately a 30 % reduction in supplemental methionine without impairing performance, while higher inclusion levels (≥80 % of the recommended level) beneficially modulated immune responses and growth-related gene expression.