The impact of copper status on lubabegron fumarate-induced growth and adipose immune cell infiltration in beef feedlot steers.

The objective of this study was to evaluate the effect of copper (Cu) status on response to lubabegron fumarate (LUB; Experior, Elanco, Greenfield, IN) and adipose tissue physiology. Forty-eight Angus crossbred steers (469 ± 31 kg) were enrolled in a 77-day finishing study, housed in pens of six, with a GrowSafe bunk (GrowSafe Systems, Ltd, Airdrie, AB, Canada) in each pen and implanted (Revalor-200, Merck Animal Health, Madison, NJ; 200 mg TBA + 20 mg E2) on day 0. A 2 × 2 factorial arrangement was applied to Cu status (Cu0, no supplemental Cu; or Cu10, 10 mg supplemental Cu/kg DM as CuSO4) and LUB (36 mg/steer/day, LUB; or no LUB, NOLUB). A prior trial resulted in steers with distinct liver Cu (Cu0 and Cu10 were 42 ± 21 and 193 ± 31 mg Cu/kg DM, respectively). Lubabegron was fed from day 37 to day 73, and cattle harvested on day 78. Weights were collected on days -1, 0, 37, 55 (mid-Experior), 76, and 77. Blood was collected on days 0, 37, 55, and 76 for non-esterified fatty acids (NEFA), glucose, and insulin. Subcutaneous adipose biopsies were collected on days 0, 37, and 66. Data were analyzed using the MIXED procedure of SAS as a factorial design, with steer as the experimental unit (n = 12 per treatment). From days 0-37, Cu0 daily gain and feed efficiency (G: F) were greater than Cu10 (P < 0.01). Overall DMI was greater in Cu10 than Cu0 (P = 0.04) and not affected by LUB (P = 0.13). Carcass-adjusted average daily gain was greater in LUB-fed cattle (P = 0.04). During the LUB period, G: F was affected by Cu × LUB (P = 0.04), where Cu0 cattle exhibited a greater improvement in efficiency due to LUB than Cu10. The revised quantitative insulin sensitivity check index displayed a LUB × Day effect (P < 0.01) where NOLUB was consistent across days and LUB had greater insulin sensitivity during the LUB period. Populations of mononuclear phagocytes were greater in Cu0-LUB over all other treatments (LUB × Cu P = 0.02). These data suggest Cu concentration influences steer response to lubabegron fumarate, highlighting the need for further research to optimize Cu supplementation to finishing cattle.