Effects of a microencapsulated blend of essential oils supplemented alone or in combination with monensin on performance and carcass characteristics of growing and finishing beef steers

Objective: A microencapsulated blend of essential oils (EO) fed to feedlot cattle was evaluated against monensin (MON) or used in association with MON and compared against MON alone or MON + tylosin (TYL). Materials and Methods: We used a randomized complete block design using weaned steers (n = 656; 254.4 +/- 7.9 kg of initial BW) assigned to 32 pens (8 replicates per treatment) and fed for 208 d. The treatments were as follows: MON + TYL (33 mg and 11 mg/kg of DM, respectively); MON (33 mg/kg of DM); EO (150 mg/kg of DM); and MON + EO (33 mg and 150 mg/kg of DM, respectively). Results and Discussion: Treatments were similar for final BW (P >= 0.24) and overall ADG (P >= 0.27). Overall DMI did not differ for MON versus EO (P = 0.93); however, MON + EO had reduced overall DMI compared with MON (P = 0.03; 9.2 vs. 9.6 kg/d, respectively) or MON + TYL (P = 0.04; 9.2 vs. 9.6 kg/d, respectively). There was no effect (P >= 0.14) on overall G:F; however, adjusted overall G:F tended to be greater for MON + EO versus MON (P = 0.08; 0.187 vs. 0.182, respectively) and for MON + EO versus MON + TYL (P = 0.07; 0.187 vs. 0.183, respectively). Carcass characteristics were similar (P = 0.11) for all treatments. Implications and Applications: Steers receiving EO had similar performance and carcass characteristics compared with steers fed MON. The MON + EO tended to improve carcass-adjusted performance compared with MON. The replacement of TYL with EO when in combination with MON may result in additional improvement in feed efficiency without changes in liver abscesses.