184 Effect of monensin intake during a stocker phase and subsequent finishing phase on performance and carcass characteristics of feedlot steers. (29th July 2019) - Weiss, Caleb P
Abstract: Three experiments were conducted to determine the effects of monensin supplementation during the stocker and finishing phase on feedlot performance and carcass characteristics of beef steers. In Exp. 1 and 2, steers (n = 61, BW = 345 ± 20 kg and n = 70, BW = 298 ± 26 kg) were fed hay and supplement or grazed wheat pasture (Exp. 1) or bermudagrass (Exp. 2) and then were transported 1, 068 km to Canyon, TX, for finishing. For Exp. 3 steers (n = 59, BW = 322 ± 31 kg) grazed wheat pasture and then transported 636 km to Stillwater, OK, for finishing. Treatments were arranged as a 3 × 2 factorial with three monensin levels during the stocker phase (0, 800, 1600 g/ton fed in a free choice mineral) and two levels during finishing [0 (UN) or 37.5 mg/kg diet DM (RUM). There were no location × treatment interactions (P ≥ 0.19) for performance or carcass measurements, therefore data were pooled across locations. Stocker × feedlot treatment interactions were not observed for performance data (P ≥ 0.50), but were observed for carcass characteristics. Cattle consuming RUM in the feedlot had decreased (P < 0.01) DMI and increased (P < 0.01) G:F compared with UN. Cattle on 1600UN treatment had the greatest LM area whereas 0U had the least (103.4 vs 96.3 cm 2 ). Steers on the 800UN and 1600UN treatments had decreased YG and 800RUM had the greatest (2.31 and 2.22 vs 2.75). Cattle consuming RUM during finishing had increased (P = 0.03) fat thickness compared to UN. Supplementation of monensin to stocker cattle may have minimal impact on subsequent feedlot performance. Providing monensin in feedlot diets still decreases DMI and improves feed efficiency of feedlot cattle.