Effect of essential oils on In vitro methane production, rumen methanogens, volatile fatty acids and feed digestibility with goat rumen liquor

Four essential oils (EOs), i.e. garlic oil (Allium sativum L., GO), garlic oil blend (Allium sativum L., GOB) clove oil (Eugenia spp., CO) and peppermint oil (Mentha piperita L., PO) at four dose levels; 0.0 g/L (D₀) 0.25 g/L (D₁), 0.5 g/L (D₂), and 1.0 g/L (D₃) of fermentation medium were evaluated for their influence on gas, methane production, rumen microbes, volatile fatty acids and feed digestibility using in vitro gas production system. Concentrate mixture and gram straw in 40:60 ratio and goat rumen liquor were used as substrate and incoculum. There was a significant (P<0.05) decrease in gas production and methane production by the addition of EOs in a dose dependent manner. The per cent inhibition in methane production (ml/g DM) was maximum with GO and ranged from 38.5–92.7 at graded doses. The higher doses of EOs were detrimental for feed digestibility. Addition of PO and CO at lowest dose (0.25g/L) had no significant effect on methane production, in vitro true dry matter (IVTD) and organic matter digestibility (IVOMD) while GO decreased methane production (ml/DDM) and IVTD by 27.20 and 3.6% The proportion (%) of propionic acid significantly increased along with decreased acetic acid with the addition of GO or GOB. Present study concluded that GO and PO have potential to reduce the in vitro methane production. However, GO at the low dose level (0.25g/L) reduced methane production significantly with little impact on IVTD.