Effect of placement weight and days on feed on feedlot cattle performance and carcass traits

Abstract

One hundred and thirty six Angus steers were used to evaluate the effects of feedlot placement weight (PW; weight of the animal at the time of its placement into the feedlot) and days on feed (DOF) on feed efficiency, carcass transfer (CT), and carcass traits. The 2 × 4 factorial experiment included PW (Light (LT), 310 kg BW; or Heavy (HV), 415 kg BW) and DOF (54, 83, 111, or 145 d) before slaughtering. At d 0, four steers selected at random from each PW group were slaughtered to determine initial hot carcass weight (HCW). The rest of the steers were allocated in pens (4 pens/treatment; 4 steers/pen) with ad libitum access to feed and drinking water. No PW × DOF interactions were detected for any response variables (P > 0.05). Heavy steers showed greater (P < 0.001) daily dry matter intake (DMI) than LT steers. Daily DMI did not change (P = 0.11) across DOF. Average daily gain (ADG) and daily carcass weight gain (CWG) were not affected (P > 0.05) by PW. Although ADG showed a quadratic (P = 0.003) response across DOF, CWG was higher (P < 0.05) for steers fed 83 d or longer. This resulted in a linear increase (P < 0.001) in CT (ratio of CWG to ADG, expressed as a percentage) during the 145 feeding period. Feed efficiency (DMI: ADG and DMI: CWG ratios) was better (P < 0.001) for LT than HV steers. The ratio DMI: ADG was higher (P < 0.05) for 145 DOF steers, whereas the ratio DMI: CWG tended (P = 0.08) to be better for 111 DOF. Heavy steers showed greater (P < 0.05) final live weight, HCW, ribeye area, subcutaneous fat thickness, and marbling score than LT steers. Final weight and HCW increased linearly (P < 0.001) with DOF. Subcutaneous fat thickness was higher (P < 0.05) for steers fed 111 d or longer. Marbling score and LM total lipid increased linearly (P < 0.001) with DOF. Longissimus muscle pH and color (a*, b*), and subcutaneous fat color (L*, a*, b*) were not affected (P > 0.05) by treatments. Warner Bratzler shear force did not differ (P = 0.16) between PW but was affected (P = 0.005) by DOF. However, all steaks showed a WBS value below 4.0 kg. Regardless of treatment, WBS decreased (P < 0.001) as postmortem aging days increased. Overall, HV steers produced larger carcasses that had greater fat deposition, and similar tenderness than LT steers. Feeding up to 111 days, regardless PW, could improve animal performance and CT, and produce large carcasses with acceptable levels of subcutaneous fat thickness and palatable beef.