Abstract
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.