Effect of nutrient intake on intramuscular glucose metabolism during the early growth stage in cross-bred steers (Japanese Black male×Holstein female)

The objective was to investigate the impact of nutrient intake during the early growth period on the expression of glucose metabolism-related genes in skeletal muscle of cross-bred cattle. From 1.5 to 5months of age, group H (n=7) animals were intensively fed a high-protein and low-fat milk replacer [crude protein (CP) 28%; ether extracts (EE) 18%; max: 2.0kg, 12l/day], and group R (n=7) animals were fed a restricted amount of normal milk replacer (CP 25%; EE 23%; max 0.5kg, 4l/day). From 6 to 10months of age, group H cattle were fed a high-nutrition total mixed ration mainly prepared from grain feed, and group R cattle were fed only roughage. Blood samples were taken from each animal at three biopsy times (1.5, 5 and 10months of age), and the blood plasma concentration of glucose and insulin was analysed. In glucose concentration, there were no significant differences; however, the concentrations of insulin were higher in group H than in group R at 5 and 10months of age. Muscle samples were taken by biopsy from longissimus thoracis muscle (LT) at 1.5, 5 and 10months of age. We analysed mRNA expression levels using the quantitative real-time polymerase chain reaction (PCR) assay for glucose transporters (GLUT1 and GLUT4), insulin receptor, phosphatidylinositol 3-kinase (PI-3K), protein kinase B (PKB, also known as Akt), hexokinase 1 (HK1) and tumour necrosis factor alpha (TNFα). Although no differences were detected at 1.5 and 5months of age, at 10months of age, GLUT1, HK1 and TNFα mRNA expression levels were significantly higher in group H than in group R. These results suggested Glut1 that affects insulin-independently mediated glucose uptake was more responsive to improved nutrition during early growth stage than GLUT4 that insulin-dependently mediated glucose uptake in LT of cattle.