Abstract
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.
Highlights
Known as 2-amino-4-methylthio butanoic acid in chemistry, methionine (Met) is usually the second or third limiting amino acid (AA) in typical swine diets [1]
The G:F of the pigs fed the Met-restricted diet was lower (P < 0.01) than that of the pigs fed the Met-adequate diet. These results indicated that a restriction of dietary SID Met by 40.5% did not affect pig feed intake, but significantly decreased their G:F and average daily gain (ADG)
This result of compromised growth performance is in line with several previous researches, such as those conducted by Bell et al [7], Chung et al [6], Ly et al [9], and Humphrey et al [16], who all reported that dietary Met restriction or deficiency can compromise pig growth performance
Summary
Known as 2-amino-4-methylthio butanoic acid in chemistry, methionine (Met) is usually the second or third limiting amino acid (AA) in typical swine diets [1]. The beneficial effects of dietary Met at an optimal level on the growth performance and meat yield of pigs have been previously reported [5, 7,8,9]; the regulatory molecular mechanisms through which Met regulates the skeletal muscle formation and growth in pigs are still unclear [1, 2]. Myogenesis is a biochemical process of muscle formation regulated by a broad spectrum of cell signaling molecules [10] which are affected by nutrient availability and nutrient metabolism [11]. Among the hierarchical interactions between those molecules and nutrient metabolites, the families of myogenic regulatory factors (MRF) and myocyte enhancer factor 2 (MEF2) for the transcription factor-mediated regulation, are key regulators of muscle growth and differentiation and have been a focus of many previous studies in humans and animals [12, 13]. Until now little is known about the effects of nutrient Met, a functional AA, on the expressions of these factor genes in pigs
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