Effect of daily rotational feeding of lasalocid and monensin to yearling feedlot steers fed in western Canada1

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.