Abstract This trial evaluated rumen protozoal population, green-house gas emissions profile, and performance in growing steers fed a proprietary essential oil blend. Growing steers (n = 36) were stratified across treatments (n = 2) using initial body weight (317 ± 34 kg). Steers were housed at the Kansas State University Beef Cattle Research Center for a 30-d training period and 70-d trial duration. Five steers were randomly selected from each treatment group (n = 10) for esophageal rumen fluid collection on d-14 and d-70. Greenhouse gas emissions profiles (CH4, CO2) were measured using Greenfeed Automated Head Chamber Systems (AHCS; C-Lock Inc., Rapid City, SD). All steers were fed a forage blend of wheatlage (83.28%), alfalfa hay (16.27%), and mineral supplement (0.45%) in an Insentec monitoring system (Insentec, Marknesse, Netherlands). A distiller grain-based supplement containing essential oil (EO) or not (CON) was offered in addition to the forage blend (0.45 kg/hd/d target). Data were analyzed in RStudio using the lmer package (fixed effect: treatment; covariate: initial body weight). The first 14-d of the trial were considered adaptation to the supplement and were not included in analysis. Average daily gain (ADG) was found to be greater in EO vs CON (1.35 kg vs 1.28 kg respectfully; P = 0.42). No difference in forage dry matter intake was observed for EO vs. CON (7.03 kg vs 6.85 kg; P = 0.74). Similarly, EO had a tendency (P = 0.06) for greater supplement intake compared to CON (0.49 kg vs. 0.47 kg respectfully). Lower methane production was found significant in EO vs. CON steers (240 g/d vs. 250 g/d; P = 0.03). Differences in CO2 production (g/hd/d) were not observed in EO steers vs. CON (7679 g/d vs. 7825 g/d; P = 0.15). Emission intensity among EO supplemented steers tended to be lower compared to CON (184 vs. 199 g CH4/kg ADG; P = 0.09). No differences (P 0.05) were observed on d-14 between Dasytrich, Isotrich and Entodiniomorph groups as a proportion of rumen protozoa population for EO compared to CON. On d-70, tendencies were observed for less Dasytrich (1.81% vs. 3.67%; P = 0.08) and Isotrich (1.03% vs. 2.82%; P = 0.06) within the identified protozoal population in EO compared to CON. Entodiniomorph populations made up a larger (P = 0.02) proportion of the protozoal population at d-70 in EO compared to CON steers (97.2% vs. 93.5%). Results suggest that animals supplemented the essential oil blend had altered rumen fermentation profiles evidenced by shifted protozoal populations at d-70 and lower methane emissions over the trial period. Numeric differences in ADG suggest a need for further adequately powered performance research to define further potential benefits of the essential oil blend.
Gibbons et al. (Wed,) studied this question.