Activity and rumination of implanted Charolais × Angus feedlot steers versus non-implanted counterparts consuming 3 levels of roughage throughout a 361-day feeding duration

Abstract

ObjectiveRumination and activity of growing feedlot steers were evaluated in response to growth-promoting implant administration, feeding duration, and dietary rough- age. Materials and MethodsCharolais × Angus steers (n = 80) were randomized to harvest (1, 42, 84, 126, 168, 210, 252, 294, 336, or 378 d on feed) and implant treatment (REV: Revalor-XS on d 0 and d 190; CON: no implant). Activity and rumination were objectively monitored via accelerometers attached to the left ear. Steers consumed 3 rations throughout the study: starter (38.5% roughage), intermediate (23% roughage), and finishing (8.5% rough- age). Data were logged in 2-h increments from 77 steers across 361 d and analyzed using mixed models. Results and DiscussionRumination and activity varied within 24-h, exhibiting bimodal patterns; rumination peaked at 0600 and 1400 h and troughed at 1000 and 1800 h. Activity peaked at 0800 and 1800 h and troughed at 0400, 1200 to 1400, and 2200 h. Steers administered REV ruminated less (331 vs. 354 min/d) than CON; however, activity was similar between treatments. Treatment × roughage interactions occurred for rumination and activity. Rumination tended to be greater for CON steers consuming 38.5% than CON steers consuming 23% roughage, furthermore, CON steers ruminated more than REV when consuming 8.5% roughage. Implanted and non-implanted steers ruminated less as roughage inclusion decreased from 38.5% and 23% to 8.5% (457 and 439 vs. 317 min/d, respectively) in the finishing ration. Activity was greatest for steers consuming 38.5% roughage and was similar between treatments; however, activity decreased upon transition to 23% and 8.5% roughage. Observed surges and declines in activity can be attributed to processing days and weather events. Implanted steers consuming 8.5% roughage were more active (342 vs. 337 and 333 min/d) than CON and REV steers consuming 23% roughage. Implications and ApplicationsIn conclusion, rumination and activity are responsive to hour of day, dietary roughage and growth-promoting implants.