Effects of yeast-based additive complex on performance, heat stress behaviors, and carcass characteristics of feedlot steers

Abstract This study was realized to evaluate the effects of a yeast-based additive complex (AC) on animal performance, heat stress behaviors, and carcass characteristics of beef steers fed in feedlot during a period of thermal heat stress. Black-hided beef steers (n = 192; initial live weight = 403 ± 24.5 kg) were used in a randomized complete block design experiment with 2 treatments; a steam flaked corn-based diet with AC (fed at 0.14 kg∙hd−1∙d−1) and a diet without AC (CON). Steers were stratified by live weight to 1 of 2 weight blocks and randomly allocated to an experimental treatment within block. Experimental supplementation was fed till d 75. Steers were fitted with an ear tag that recorded rumination and activity in 2-h intervals; whereas heat stress behaviors were recorded in 1-min intervals. Pen was used as the experimental unit for animal performance, carcass characteristics, and rumination, and animal was used for heat stress behaviors, while day was used as repeated measure for the analysis of heat stress behaviors and rumination. Data were analyzed using the MIXED procedure of SAS. Final live weight (LW), average daily gain (ADG), dry matter intake (DMI), and gain:feed (G:F) were not affected (P > 0.38) by treatment (d 1-76). Time spent ruminating (min/d) were not affected by AC supplementation (P ≥ 0.21). Treatment did not influence (P > 0.13) time spent panting, resting, or eating. Supplementation of AC did not impact (P ≥ 0.22) HCW, fat thickness, Longissimus area, or marbling score . Dressing percentage was decreased (P = 0.02) with AC addition (60.4% ± 0.6) compared to CON (61.0% ± 0.6) and calculated yield grade tended (P = 0.09) to increase with AC (2.51 ± 0.16) compared to CON (2.37 ± 0.16). Overall, feedlot performance, efficiency and carcass characteristics were not influenced by the supplementation of AC. Supplementing cattle exposed to thermal heat stress with AC did not impact rumination or panting behaviors.