Effects of post-weaning exposure to a high-concentrate diet vs. pasture on live performance, carcass characteristics, and meat quality of early harvested steers

Abstract Text: Twenty Angus steers (261 ± 21.5 kg) were used to evaluate the effect of post-weaning feeding strategy on live performance, carcass characteristics, and meat quality.  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.  At slaughter, subcutaneous adipose tissue samples were collected from each steer and flash frozen for later analysis.  The 6–12 rib section of each carcass was collected for further analysis on day 2 post-harvest. Steers consuming a high-concentrate based diet had a greater overall ADG than P ones (1.36- vs. 0.68-kg/d; P < 0.0001) resulting in heavier final BW and HCW, and greater dressing percentage (P < 0.001). Steers consuming grain had larger ribeye area (P = 0.0006) and more fat at the 12^th rib (P < 0.0001) than steers on forages, whereas there were no differences for KPH and calculated yield grade (P = 0.22). The high-concentrate based diet resulted in much greater marbling scores than grazing high-quality forages (P < 0.0001; 448 vs. 240).  Despite the increased marbling, there was no difference in longissimus muscle (LM) b* (P = 0.956), whereas LM from F were brighter and more red (greater a*; P < 0.003).  Both subcutaneous L* and b* were not different between treatments (P = 0.20), whereas subcutaneous a* was greater for F than P (P = 0.0018).  Fat cell sizes of subcutaneous tissue were larger in perimeter and area for F (P < 0.0001) whereas P had a greater fat cell number (P < 0.0001).  Steers on F had greater LM total lipid (P < 0.0001), whereas P resulted in greater moisture, nitrogen and ash (P < 0.0001). There were no differences in SFA or PUFA n-6 in LM (P = 0.49) whereas F had greater MUFA (P = 0.0037) and P had greater PUFA and PUFA n-3 percentages (P < 0.01) resulting in a more desirable PUFA n-6/PUFA n-3 ratio (P= 0.0003; 1.46 v 7.35 for P and F, respectively). This suggests that exposure to high-concentrate based diets early in the finishing process results in increased performance and carcass quality, along with deposition of intramuscular adipose tissue.

Keywords: Grain, Pasture, Meat Quality