Abstract A finishing study was conducted to evaluate the physiological and molecular responses of beef steers to lubabegron (LUB; Experior®, Elanco Animal Health) supplementation. Thirty-two crossbreed steers (524 ± 5 kg) were randomly assigned to control (CON) or LUB diets (3.2 g/ton DM) for 63 d. Growth performance, carcass characteristics, serum chemistry, longissimus muscle (LM) composition, gene expression, and signaling protein abundance were assessed. Lubabegron supplementation increased final BW (637 vs. 612 kg; P 0.01), ADG, DMI, and feed efficiency relative to CON. Hot carcass weight was increased by 18.5 kg in LUB cattle (P 0.01), whereas dressing percentage, ribeye area, 12th-rib fat thickness, yield grade, and marbling score were unaffected. Longissimus protein percentage was higher (23.6 vs. 22.5%; P 0.01) and fat decreased (5.0 vs. 6.4%; P = 0.05) in LUB steaks. Warner-Bratzler shear force was greater in LUB samples at both 2 days (4.36 vs. 3.67 kg; P = 0.03) and 14 days (3.74 vs. 2.76 kg; P 0.01) postmortem. Serum analyses revealed increased creatinine, total protein, bilirubin, and cholesterol (P 0.01) in LUB steers, consistent with altered nitrogen and lipid metabolism. Transcriptomic profiling at day 56 revealed 643 differentially expressed genes, with upregulation of myogenic and glycolytic pathways and downregulation of lipid metabolism genes. Western blotting confirmed greater phospho-mTOR abundance (P 0.01) and a trend for higher Akt phosphorylation (P = 0.08), with a tendency toward reduced AMPK activation (P = 0.09). Therefore, LUB enhances growth performance and carcass weight in finishing steers, accompanied by transcriptional and signaling adaptations in skeletal muscle that favor protein accretion while limiting lipid deposition.
Munger et al. (2026) studied this question.