Antimethanogenic and Antiprotozoal Effect of Some Essential Oils in Vitro

Ruminal inoculum enriched with particle-associated microorganisms was collected from rumen cannulated Santa Inês wethers grazing tropical grass pasture and a supplement based on ground corn and soybean before feeding and used to evaluate effects of some commercial essential oils (EO) on ruminal fermentation and methane emission in vitro. The investigated EOs were orange EO (Citrus sinensis, CrS25, CrS50, CrS75), lemon EO (Citrus limonum, CrL25, CrL50, CrL75), mint EO (Mentha arvensis L., MeA25, MeA50, MeA75) and garlic EO (Allium sativum L., AS25, AS50, AS75), which supplemented to basal diet by four levels (0, 25, 50 and 75 μl/75ml buffered rumen fluid). The results showed that the Citrus limonum, Mentha arvensis and Allium sativum essential oils were decreased significantly cumulative gas production (GP), while Citrus sinensis essential oil had no significant effect on cumulative GP. The Citrus limonum and Mentha arvensis essential oil decreased (P<0.01) methane emission by 40 and 38%, respectively, while the third dose of Mentha arvensis and all doses of Allium sativum essential oil supplementation completely inhibited methane emission compared to the control diet. The reduction in methane emission was accompanied with decreases in true degradation of dry and organic matter, total protozoa count, short chain fatty acids but improved the partitioning factor (index of the microbial protein synthesis efficiency) and no significant differences in NH3-N concentrations compared to the control diet. It is concluded that Citrus limonum essential oil had potential effects as antimethanogenic and antiprotozoal without detrimental effects on rumen degradation and fermentation in vitro.