Dose-response effects of sage (Salvia officinalis) and yarrow (Achillea millefolium) essential oils on rumen fermentation in vitro

This study aimed at determining the chemical composition of sage essential oil (SEO) and yarrow essential oil (YEO), and investigate in vitro their impacts on gas production kinetics, ruminal digestibility and fermentation, and rumen methanogenesis at different dosages (0, 250, 500 and 750 mg L^-1 for SEO; and 0, 250, 500, 750 and 1000 mg L⁻¹ for YEO). Alpha-pinene and 1,8 cineol were two major constituents of both SEO and YEO. Both SEO and YEO had a linear and quadratic effect on asymptotic gas production (P<0.05). The gas production rate increased linearly with SEO and curve-linearly with YEO dosages (P<0.05). In vitro degradability of dry matter and organic matter decreased only by YEO. The partitioning factor (PF) and the microbial biomass (MB) decreased and increased linearly with YEO and SEO dosages, respectively (P<0.05). Total volatile fatty acids (VFA ) were not affected by SEO, but decreased in a linear and quadratic manner with YEO dosage (P<0.05). The VFA pattern was modified in a linear and quadratic manner by both SEO and YEO (P<0.05). Ammonia concentration increased linearly only with YEO increasing doses. The methane to total gas (TG) ratio decreased quadratically only by SEO with reductions of 6.7, 13 and 4.2% at the doses of 250, 500 and 750 mg L⁻¹, respectively. These results revealed that SEO modifies the rumen fermentation positively towards producing more MB and less methane in the dose range of 0-750 mg L⁻¹, however, YEO adversely affected the rumen fermentation at all the tested doses.