In vitro study the effects of different levels of oregano (Origanum vulgare) essential oils on ruminal fermentation parameters, methane production and rumen induced acidosis

Theaim of the current study was to assess effects of different levels of Origanum vulgare (0, 250, 500, 750 and 1000 mg/L) on kinetics of gas production, some ruminal digestion and fermentation parameters, methane production and also to determine its potential in controlling rumen acidosis using in vitro method in four separate phases. In the first phase, the asymptote of gas production (A) and gas production rate (b) were changed nonlinearly and lag phase (L) increased linearly with increasing doses of oregano essential oils (P<0.0). The highest A and b and the lowest L were observed at 250 mg/L of the essential oil. In the second phase, the in vitro true dry matter (IVTDMD) and organic matter (IVTOMD) degradability, and total volatile fatty acids (TVFA) concentration decreased at doses higher than 500 mg/L. However, the gas produced after 24 h of incubation (GP24) and microbial biomass (MB) were increased at doses up to 750 mg/L. The molar proportion of acetate and propionate increased and that of butyrate decreased at doses higher than 500 mg/L. Using oregano essential oil resulted also in a nonlinear decrease in concentration and percentage of produced methane, but had no effect at any of the used doses in controlling rumen acidosis.