Abstract

Abstract A serial-harvest study was conducted to evaluate rumination and activity of growing steers in response to implant and dietary roughage. Charolais×Angus steers (n = 80) were randomized to harvest (0, 42, 84, 126, 168, 210, 252, 294, 336 or 378 DOF) and implant treatment (REV: Revalor-XS on d-0 and d-190 or CON: no implant). Activity and rumination were objectively monitored by SCR accelerometers attached to the left ear. Steers consumed 3 rations throughout the study: starter (38.5% roughage), intermediate (23% roughage), and finishing (8.5% roughage). Data was logged in 2-h increments from 77 steers across 361 d and analyzed using mixed models. Rumination and activity varied (P < 0.01) 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, 1200–1400, and 2200 h. Steers administered REV ruminated less (364 vs 380 min/d; P = 0.04) than CON; however, 24-h activity was similar (P = 0.29) among treatments. Treatment×roughage interactions (P < 0.01) occurred for rumination and activity. Rumination tended to differ (P = 0.06) between CON consuming 38.5% and 23% roughage, however, CON steers ruminated (P < 0.01) more than REV when consuming 8.5% roughage. Implanted and non-implanted steers ruminated less (P < 0.01) as roughage inclusion decreased from 38.5% and 23% to 8.5% (457 and 439 vs 317 min/d) in the finishing ration. Activity was highest for steers consuming 38.5% roughage and was similar (P > 0.05) among treatments; however, activity decreased (P < 0.01) upon transition to 23 and 8.5% roughage. Activity peaks and troughs 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; P < 0.01) than CON and REV steers consuming 23% roughage. In conclusion, rumination and activity are responsive to hour, dietary roughage and growth-promoting implants.

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