Methionine improves the performance and breast muscle growth of broilers with lower hatching weight by altering the expression of genes associated with the insulin-like growth factor-I signalling pathway

The present study aimed to investigate the responses of broilers with different hatching weights (HW) to dietary methionine (Met). A total of 192 1-d-old Arbor Acres broiler chicks with different HW (heavy: 48 center dot 3 (sem 0 center dot 1)g and light: 41 center dot 7 (sem 0 center dot 1)g) were allocated to a 2 (HW)x2 (Met) factorial arrangement with six replicates of eight chicks. Control starter (1-21d) and finisher (22-42d) diets contained 0 center dot 50 and 0 center dot 43% Met, respectively. Corresponding values for a high-Met treatment were 0 center dot 60 and 0 center dot 53%. Light chicks had poorer (P<0 center dot 05) growth performance and breast muscle weight and lower (P<0 center dot 05) insulin-like growth factor-I (IGF-I) concentration and mRNA level in breast muscle than heavy chicks when both were fed the control diets. High-Met diets improved performance and promoted breast muscle growth and IGF-I concentration in light chicks (P<0 center dot 05). Increased IGF-I and target of rapamycin (TOR) mRNA levels as well as decreased eIF4E-binding protein 1 (4EBP1), atrogin-1 and forkhead box O 4 (FOXO4) mRNA levels were induced by high-Met diets in light chicks (P<0 center dot 05). In conclusion, the Met requirement of broilers might depend on their HW and Met levels used in the control diets in the present study were adequate for heavy chicks but inadequate for light chicks, resulting in poorer performance and breast muscle growth, which were improved by increasing dietary Met supply presumably through alterations in IGF-I synthesis and gene expression of the TOR/4EBP1 and FOXO4/atrogin-1 pathway.