Impact of geranium essential oil as a sustainable feed additive on <i>in vitro</i> rumen gas and methane production, nutrient degradability and fermentation efficiency

Abstract This study determined the effects of geranium essential oil (0%, 0.5%, 1%, and 1.5%) on the in vitro ruminal fermentation of a ruminant diet consisting of 60% concentrate and 40% forage. Gas production (GP), carbon dioxide (CO 2 ), methane (CH 4 ), total and individual short-chain fatty acids (SCFAs), and nutrient degradability were measured. The 1.5% essential oil inclusion resulted in the highest (P&lt;0.001) asymptotic GP, followed by 1.0% and 0.5%, which produced similar results. The inclusion of 1.5% essential oil produced the highest cumulative CH 4 production during the incubation period; however, after 48 h, it resulted in the lowest (P=0.025) CH 4 proportion relative to total gas, indicating a shift in fermentation dynamics. Geranium essential oil supplementation significantly increased (P&lt;0.001) asymptotic CO 2 production compared to the control. The control group had the lowest (P≤0.011) degradability of dry matter, neutral detergent fiber, and acid detergent fiber, while the 1.5% inclusion resulted in the highest degradability. The diet containing 1.5% essential oil also had the highest (P&lt;0.05) levels of acetate, propionate, and metabolizable energy. In conclusion, the addition of 1% to 1.5% geranium essential oil to ruminant diets can improve nutrient digestibility, and rumen fermentation, and reduce CH 4 production.