Evaluation of essential oil supplementation as a feed additive on rumen fermentation characteristics and methane mitigation in ruminants: A meta-analysis

This research aimed to investigate the use of essential oils (EO) in vivo as a feed additive on rumen fermentation characteristics and methane gas through a meta-analysis approach by integrating various related studies. The data analyzed came from 21 journals, 26 studies, and 73 data points from 2007–2021, which were tabulated using Microsoft Excel and analyzed with SAS using the mixed model method. The results of EO supplementation exhibited a significant (P < 0.01) decrease in ammonia concentration, Diplodinium population, and methane gas production, as well as a significant (P < 0.05) reduction of acetate proportion and Dasytrica populations. In contrast, EO supplementation had a significant effect (P < 0.01) on final body weight increase. The crude protein tended to increase (P < 0.1) with EO supplementation. In conclusion, EO supplementation as a feed additive can positively affect rumen fermentability and methane gas production.