The Effect of Lubabegron Fumarate Feeding Duration on the Growth Performance and Carcass Characteristics of Finishing Steers

Angus-cross steers (n = 180; 483 kg ± 56.9 initial BW) were used in a finishing trial to determine the effect of lubabegron fumarate (Experior 10, Elanco; Greenfield, IN, USA) feeding duration on growth performance and carcass characteristics. Steers were stratified by BW into 36 pens (5 steers/pen; 9 pens/treatment). Lubabegron fumarate treatments were: CTRL – no lubabegron fumarate supplementation; LUB21 – lubabegron fumarate supplementation for the last 21 DOF; LUB49 – lubabegron fumarate supplementation for the last 49 DOF; and LUB77 – lubabegron fumarate supplementation for the last 77 DOF. Lubabegron fumarate was fed at a rate of 36 mg/steer·d−1. Data were analyzed as a randomized complete block design using Proc Mixed SAS 9.4. Fixed effects were treatment and block. Pen was the experimental unit. Ultrasound images were captured on a subset of steers (n = 80) at d 21, 49, 77, and 98. Initial ultrasound IMF score was used as a covariate. Final shrunk body weight was greatest in LUB49 and LUB77 compared to CTRL (P = 0.02) with LUB21 intermediate. Lubabegron fumarate treatment did not influence overall DMI (P = 0.90). Regardless of duration, lubabegron fumarate tended to increase overall ADG, where all supplemented treatments were similar and greater than CTRL (P = 0.09). Similarly, all lubabegron fumarate supplemented treatments had greater overall G:F compared to CTRL (P = 0.01). Lubabegron fumarate treatment did not influence dressing percent or yield grade (P ≥ 0.19). Feeding lubabegron fumarate for 49 or 77 days prior to harvest resulted in increased HCW (P = 0.02) compared to CTRL, with LUB21 being intermediate. When lubabegron fumarate was fed for 77 days prior to harvest, a reduction in marbling score was noted (P = 0.01) compared to LUB49, LUB21, and CTRL. Rib fat thickness tended to be less in LUB77 compared to LUB21 (P = 0.09), with LUB49 and CTRL being intermediate. Ribeye area tended to be greater in LUB49 and LUB77 compared to CTRL (P = 0.06) with LUB21 being intermediate. Lubabegron fumarate treatment did not influence overall ultrasound ribeye area or rib fat thickness (P ≥ 0.26), although a DAY effect (P = 0.01) was noted where these measures both increased over time. A TRT × DAY effect (P = 0.02) was noted for ultrasound intramuscular fat where ultrasound intramuscular fat score increased over time for all treatments except LUB77, which plateaued from d 77 to 98. These results indicate lubabegron fumarate supplementation improves ADG, feed efficiency, and HCW. Additionally, these results suggest feeding lubabegron fumarate for 49 or 77 d prior to harvest may best allow for optimal HCW response; however, when fed for 77 d, detrimental effects on marbling score were observed.