Effect of daily rotational feeding of lasalocid and monensin to yearling feedlot steers fed in western Canada11Funding provided by Zoetis Canada Inc., Kirkland, QC, Canada

Improvements in feed conversion of almost 6% were noted when monensin and lasalocid were rotated at various intervals in reports from the late 1980s and early 1990s. If true, such a response would hold large economic implications for cattle feeders in western Canada. Thus, yearling steers (n = 10,012; 36 pens; initial BW: 438.8±8.1 kg) fed at 2 commercial feedlots in Alberta, Canada, were used to evaluate the effect of daily rotation of lasalocid (36 mg/kg) and monensin (25 mg/kg; ROT) compared with daily feeding of monensin only (25 mg/kg; CTRL) on performance, carcass, and health variables. Steers were fed finishing diets based on dry-rolled or temper-rolled barley grain until slaughter (112.6±23.1 d). There were 18 replicates per experimental group, and the single-pen lot was the experimental unit (36 single-pens lots; 278 ± 54 steers per single-pen lot). Carcass-adjusted ADG were greater (P < 0.01) by 4.81% for ROT compared with the CTRL group. Improvements in ADG were partially driven by greater DMI (P = 0.02) for ROT (11.60 kg/d) compared with CTRL (11.35 kg/d). Carcass-adjusted G:F was also increased by 2.72% (P < 0.01) for ROT compared with CTRL. No differences were observed (P ≥ 0.06) between ROT and CTRL for Canadian QG and USDA YG. No differences were detected in mortality rates (P ≥ 0.21) between experimental groups. Rotational feeding of lasalocid and monensin improved feedlot performance and had minimal effects on carcass characteristics and animal health parameters compared feeding of monensin alone.