The supplementation of lubabegron or ractopamine hydrochloride in the summer improved growth performance but did not impact rumination, mobility scores, and behaviors in feedlot cattle in the United States†.

This study evaluated the effects of β-ligand supplementation on growth performance, carcass characteristics, rumen parameters, mobility, and behavior in feedlot steers finished in the summer months. Three hundred sixty Angus crossbred steers were ranked by body weight (BW) and randomly assigned to one of three treatments: 1) Control (no β-ligand), 2) Ractopamine Hydrochloride (RAC; 300 mg·animal-1·d-1), or 3) Lubabegron (LUB; 36 mg·animal-1·d-1). RAC and LUB were fed for the final 35 d of the finishing period, followed by a 4 d voluntary withdrawal period prior to slaughter. Steers were housed in feedlot pens (10 head/pen; 12 pens/treatment). A steam flaked corn-based diet with the appropriate treatment was delivered once daily to provide cattle ad libitum access to feed over a 24 h period. Body weights and mobility scores were obtained at the beginning of the experiment and every 14 d throughout the supplementation period. Weekly in-pen behavior was observed via 24 h video footage, using instantaneous sampling with a 10-minute scan interval. Rumen boluses were administered to 2 steers per pen before the initiation of the experiment to continuously monitor reticulorumen temperature, pH, and rumination events. Ambient environmental conditions were recorded throughout the study. Post-slaughter carcass characteristics were evaluated. The RAC and LUB supplemented steers had greater (P < 0.05) final BW, average daily gains, and feed efficiencies compared to controls. Steers supplemented with RAC and LUB had greater (P < 0.05) hot carcass weights and longissimus muscle areas than control steers. No treatment differences (P > 0.05) were detected for dressing percentage, quality grade, subcutaneous fat depth, USDA yield grade, and meat color. There was no treatment effect (P > 0.10) for reticulorumen pH, temperature, or rumination time. Similar (P > 0.05) mobility score distributions were observed across treatments. The majority of cattle exhibited normal mobility over the course of the study. Three-way interactions (P < 0.01) between treatment, week, and time of day were observed for drinking, standing, and lying behaviors. A two-way interaction (P < 0.05) between treatment and week was detected for locomotion behavior. In summary, RAC and LUB supplementation to feedlot steers during the summer months improved growth performance and carcass characteristics and had no impact on mobility scores, rumen parameters, or behaviors when compared to control steers.