Abstract
A 42-day study evaluated the efficacy of crystalline DL-methionine (DL-Met) at the recommended level (control) versus microencapsulated DL-methionine (CM) at 60%, 70%, 80%, 90%, and 100% of the commercial recommended levels (CM60, CM70, CM80, CM90, and CM100) in broiler chickens. A total of 1,260 one-day-old Arian broiler chicks were assigned to 6 experimental groups with 7 replicates of 30 chicks per group. The results showed that average daily gain (ADG) and the European performance index were significantly higher in the Control, CM80, CM90, and CM100 groups compared to CM60 during the 22-42-day period and over the entire 1-42-day period (P < 0.05). CM90 also outperformed the Control and CM70 in ADG (P < 0.05), and feed conversion ratio was significantly improved in CM80, CM90, and CM100 compared to the Control (P < 0.05). Ileal digestibility of dry matter and crude protein improved in CM80 and higher treatments, with AMEn also higher in CM80 to CM100 compared to CM60 (P < 0.05). In the ileum, CM90 and CM100 increased populations of anaerobic bacteria and Lactobacillus, while reducing Coliform populations (P < 0.05). Histomorphological indices, including villus height and surface area in the jejunum and villus height-to-crypt depth ratio in the ileum, were enhanced in intermediate-to-high CM treatments. Gene expression analysis revealed that NF-kB and IL-6 expression were significantly lower in CM90 and CM100 compared to other treatments, except CM80 (P < 0.05). IL-10 expression was higher in CM80, CM90, and CM100 compared to CM60 (P < 0.05), while no significant differences were observed for IL-1β and IFN-γ between all treatments (P > 0.05). Economically, CM60 had the lowest feed cost but resulted in reduced net profit and efficiency. In contrast, CM80 to CM100, particularly CM90, improved economic returns through higher income and reduced feed cost per unit of weight gain (P < 0.05). In conclusion, replacing crystalline methionine with microencapsulated methionine at 80-90% of the commercial recommendation improved growth performance, gut health, immune modulation, and economic returns.