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

Abstract

Angus-cross steers (n = 180; 483 kg ± 56.9 [SD] 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 outcomes. Steers were stratified by BW into 36 pens (5 steers/pen; 9 pens/treatment) and assigned 1 of 4 treatments: no lubabegron fumarate (LUB) supplementation (CTRL), or LUB supplementation on the last 21 (LUB21), 49 (LUB49), and 77 (LUB77) days prior to harvest. All LUB treatments received 36 mg/steer·d−1 with a 4-day withdrawal prior to harvest. Body weights, blood, and ultrasound measurements were collected throughout the study. Serum glucose, NEFA, and insulin were used to calculate revised quantitative insulin sensitivity check index (RQUICKI) (De Sousa et al., 2022). Estimated ultrasound empty body fat (EBF) % was calculated using equations from Guiroy et al. (2002) and Tatum et al. (2012). Data were analyzed as a randomized complete block design and repeated measures using Proc Mixed SAS 9.4. Steers fed LUB for 49 or 77 days had greater final shrunk body weight (P = 0.01) and HCW (P = 0.02) compared to CTRL steers with LUB21 being intermediate, while DMI was unchanged (P = 0.90). Feeding LUB tended to increase overall ADG (P = 0.09) and enhance G:F (P = 0.01) compared to CTRL. Estimated ultrasound EBF% was the least for LUB77 (P < 0.01). Feeding LUB for 77 days reduced marbling score compared to the other treatments (P < 0.01). Rib fat thickness tended to be lower in LUB77 compared to LUB21 (P = 0.09), while REA tended to be greater in LUB49 and LUB77 compared to CTRL (P = 0.06). No TRT × DAY effect interactions were observed for ultrasound intramuscular fat, rib fat, or ribeye area (P ≥ 0.13), although DAY effect (P < 0.01) indicated these measures increased over time. Serum NEFA concentrations were lower in LUB77 than in CTRL, LUB21, and LUB49 (P = 0.03), whereas insulin concentrations tended to be lower in LUB49 and LUB77 than in CTRL (P = 0.09), with LUB21 intermediate. Overall, LUB supplementation improved G:F without affecting DMI; LUB49 and LUB77 increased FSBW and HCW relative to CTRL, with LUB21 intermediate. Feeding LUB for 77 d reduced marbling score, whereas no statistically detectable reduction relative to CTRL was observed with 21 or 49 d of supplementation.