Evaluating in vitro dose-response effects of Lavandula officinalis essential oil on rumen fermentation characteristics, methane production and ruminal acidosis

Four in vitro experiments (Exp.) were conducted to evaluate lavender essential oil (LEO) effects at 0 (control), 250 (low dose), 500 (medium dose), 750 and 1000 µL per L (high doses) of incubation medium on rumen gas production kinetics (Exp.1), ruminal digestibility and fermentation (Exp.2), methane production (Exp.3) and rumen acidosis (Exp.4). The asymptote of gas production (A) increased quadratically (p < 0.001), but the lag phase (L) increased (p = 0.003), and gas production rate (µ) decreased linearly (p = 0.031) with increasing dose of LEO. A linear and quadratic effect (p < 0.01) was observed for the gas produced after 24 hr of incubation (GP24). In vitro true dry matter degradability (IVTDMD) and in vitro true organic matter degradability (IVTOMD) both decreased linearly (p < 0.01), but microbial biomass (MB) and partitioning factor (PF) changed quadratically with increasing doses of LEO (p < 0.05). A cubic effect was observed for total volatile fatty acid (TVFA) and ammonia (NH3) concentrations (p < 0.05). Acetate molar percentage decreased (p = 0.004), whereas those of butyrate and valerate increased linearly (p < 0.05) with LEO dosage. The molar percentage of propionate increased by 10.60 and 12.00% at low and medium doses of LEO, respectively. Methane production decreased by 11.00 and 44.00 to 60.00% at medium and high doses of LEO (p < 0.05), respectively. Lavender essential oil decreased also ruminal pH at all included doses (p < 0.05), intensifying rumen acidosis. These results revealed a dose-dependent selective effect (stimulatory at low and medium, and inhibitory at high doses) of LEO on rumen fermentation.