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Effects of post-weaning exposure to a high-concentrate diet vs. pasture on carcass ultrasound, plasma insulin and glucose, and gene expression of lipogenic enzymes of early harvested steers
Twenty Angus steers (261 ± 21.5 kg) were used to evaluate the effect of post-weaning feeding strategy on plasma insulin and glucose levels and gene expression of lipogenic genes. Steers were randomly assigned to one of two feeding treatments: high-concentrate based diet (cracked corn, corn silage, and soybean meal [F]) or high-quality pasture (winter annuals, alfalfa, and non-toxic fescue [P]) for 127-d. Blood samples were collected at 21-d intervals. At slaughter, s.c. adipose tissue samples were collected from each steer and flash frozen in optimal cutting temperature compound for later histology. Steers consuming a high-concentrate based diet had a greater overall ADG (1.36- vs. 0.68-kg/d for F and P, respectively; P < 0.0001) resulting in heavier final BW and HCW (P < 0.001). There was an interaction of treatment and time for ultrasound ribeye area (REA) and 12th-rib fat thickness (P < 0.014) as F resulted in increased REA and fat deposition over time whereas P did not differ over time. Similarly, there was a treatment by time interaction for plasma insulin with insulin levels of steers consuming a high-concentrate based diet increasing over time while steers grazing forages did not. There was no interaction of treatment and time on glucose (P = 0.469) whereas steers on F had greater plasma glucose than those on P (P < 0.0001). RefFinder was used to evaluate reference gene candidates. Thy1 was selected as the most stable reference gene. There was no difference in the expression of acetyl CoA carboxylase, elongase-6, leptin, or glucose transporter type 4 (P > 0.14). Fatty acid synthase and stearoyl CoA desaturase-9 were upregulated by 16 and 81 fold, respectively for steers on F when compared to P (P < 0.002). Additionally, steers receiving a high-concentrate based diet had a 42-fold increase in mRNA of elongase-5 compared to steers grazing high-quality forages (P = 0.0006) and 3-fold more expression of lipoprotein lipase (P = 0.011). Early exposure of steers post-weaning to high concentrate diets increased the ratio of insulin to glucose and marbling deposition with greater expression of lipogenic genes.
Keywords:
Gene Expression, Insulin, Glucose