Influence of lemongrass and oregano essential oils and their combination on in vitro ruminal fermentation and greenhouse gas emissions in total mixed ration for dairy cows

Ruminants play a crucial role in the food chain, but are also considered contributors of greenhouse gas (GHG) emissions. Essential oils (EOs) are emerging as natural feed additives in ruminants’ nutrition to enhance animal health, performance and reduce environmental footprint. Among EOs, lemongrass (Cymbopogon winterianus) and oregano (Origanum vulgare) EOs (LEO and OEO) have attracted attention as modulators of ruminal fermentations, but their role needs to be clarified. The experiment was designed using a randomised setup to assess the effects of LEO and OEO on in vitro ruminal fermentation and GHGs, using total mixed ration (TMR) as substrate (incubation time 24h). Experimental treatments included (doses as % of TMR on DM basis): 1) control only TMR (0% EOs) 2) 0.07% LEO 3) 0.07% OEO 4) 0.035% LEO + 0.035% OEO 5) 0.07% LEO + 0.07% OEO. Each treatment was repeated three times in two experimental runs. Only EO combinations reduced total gas (−9%, p=0.001). All EOs decreased CO2 emissions by −5 to −12% with no significant differences between treatments (p<0.001), although anti-methanogenic effects were not observed (p=0.192). Volatile fatty acids were slightly affected only by EOs blend at the highest dose, resulting in a reduction of propionate (−1.3%, p=0.02), an increase in acetate:propionate (+0.16%, p=0.04) and isovalerate (+0.7%, p=0.03). LEO reduced pH (−0.6%, p=0.004), while OEO increased oxidation capacity (+4.2%, p=0.004), but both parameters remained within physiological ranges. Canonical discriminant analysis confirmed distinct EOs effects, highlighting their potential as natural additives for improving ruminal fermentation and mitigating ruminant environmental footprint.