THE EFFECT OF LUBABEGRON FUMARATE FEEDING DURATION ON ESTIMATED NITROGEN UTILIZATION AND GREENHOUSE GAS EMISSIONS INTENSITY IN FINISHING STEERS

Abstract

Angus-cross steers (n = 180; 483 kg ± 56.9 initial BW) were used in a finishing trial to evaluate the effects of lubabegron fumarate (Experior 10, Elanco; Indianapolis, IN, USA) feeding duration on serum urea nitrogen (SUN), estimated nitrogen excretion, nitrogen use efficiency and estimated greenhouse gas emissions intensity. Steers were stratified by BW into 36 pens (5 steers/pen; 9 pens/treatment). Treatments included: 1) no lubabegron fumarate (LUB) supplementation (CON), or LUB supplementation for the last 2) 21 (LUB21), 3) 49 (LUB49), and 4) 77 (LUB77) days on feed. Lubabegron fumarate was fed at a rate of 36 mg/steer·day−1. Data were analyzed as a randomized complete block design using PROC MIXED in SAS 9.4 with treatment and block as fixed effects and pen as the experimental unit. Variables measured over multiple days were analyzed using a repeated measures mixed model with day 21 values included as a covariate. Equations incorporating collected data and feeding practices were utilized to estimate protein utilization and carbon dioxide equivalents between treatments (UpLook™, Elanco Animal Health). A TRT × DAY effect was observed for SUN (P = 0.01) with all treatments, except LUB21, having increased SUN concentrations by day 98. It was observed that following treatment initiation, the respective treatment group had reduced SUN concentrations by the next collection date. A TRT × DAY effect was observed for estimated urinary nitrogen (UN; P = 0.01). All treatments remained similar between days until day 98 when both LUB21 and LUB49 had reduced estimated UN excretion (P = 0.01). Lubabegron supplementation increased net protein gain, carcass nitrogen gain, and nitrogen use efficiency compared with CON (P ≤ 0.03) and reduced estimated finishing emissions per kg of live weight, gain, and carcass weight (P ≤ 0.04). Under these experimental conditions, these data indicate that supplementation of LUB improved indicators related to nitrogen utilization, ammonia production, and greenhouse gas emission intensity. These results provide insight into how the duration of LUB supplementation within the approved feeding period influences N use efficiency and estimated greenhouse gas emissions intensity outcomes.