RESUMO
Background: Methionine (Met) is usually the second or third limiting amino acid in swine diets and plays vital roles in promoting the growth, especially, the muscle growth of pigs. This research evaluated the effects of dietary Met restriction on the growth performance, plasma metabolite concentrations, and myogenic gene expression in growing pigs. Materials and methods: Eight genes in two families (myogenic regulatory factor family and myocyte enhancer factor 2 family) were selected for the analysis. Twenty individually penned barrows (crossbred, 23.6 ± 2.4 kg) were randomly allotted to two dietary treatments (n = 10). A diet based on corn and soybean meal (Diet 1, Met-restricted) was formulated to meet or exceed the energy and nutrient requirements, except for Met. Diet 2 (Met-adequate) was formulated by adding crystalline DL-Met to Diet 1 to meet the Met requirement. During the 4-week feeding trial, average daily gain (ADG), average daily feed intake (ADFI), and gain to feed ratio (G:F) were measured. Immediately before and after the feeding trial, blood was sampled via jugular venipuncture for plasma nutrient metabolite analysis, while Longissimus dorsi muscle were sampled via aseptic biopsy for gene expression analysis. Data were analyzed with Student t-test. Results: Pigs fed the Met-restricted diet had lower ADG and G:F (P < 0.01). Plasma Met, cysteine, and taurine concentrations were lower (P < 0.05), while glycine and histidine concentrations were higher (P < 0.05), in pigs fed the Met-restricted diet. Furthermore, the pigs fed the Met-restricted diet tended to express less myogenic factor 6 (Myf6) and myocyte enhancer factor 2D (Mef2D) mRNA in longissimus dorsi muscle (P < 0.09). Conclusion: Given the fact that Myf6, assisted by Mef2D, is involved in myocyte differentiation, this study suggests that the reduced growth performance in the Met-restricted pigs may be associated with a reduced muscle cell differentiation.
