Effect of combination of essential oils on in vitro methane production, volatile fatty acid fractions and feed digestibility with goat rumen flora

Different combination of garlic oil (GO from Allium sativum L.), clove oil (CO from Eugenia spp.) and peppermint oil (P from Mentha piperita L.) as GO+PO (1:1), GO+CO (1:1), CO+PO (1:1) and GO+PO+CO (1:1:1) was evaluated in in vitro gas production test for their effect on total gas production, methane production, dry matter organic matter digestibility and volatile fatty acid fractions. The addition level was low (D1) at 0.25 g/L, medium (D2) at 0.5 g/L, and high (D3) at 1.0 g/L of fermentation medium. Concentrate mixture and bengal gram straw (Cicer arietinum L.) in 40:60 ratio was incubated with incubation medium containing goat rumen liquor for 24 h at 39°C in glass syringes. Three goats fed with concentrate pellet and Bengal gram straw served as donor of the rumen liquor. In vitro fluid pH varied between 6.50 to 6.59. Total gas production (mL/g DM) in control group was 154.07, at lower dose level (0.25 g/L) there was increase in gas production which significantly decreased at highest dose level. There was significant (P<0.05) decrease in the methane production (mL/g DM and mL/g DDM) on GO and PO supplementation together. At low dose level (D1, 0.25g/L) there was no statistically (P>0.05) significant difference in in vitro dry matter and organic matter digestibility with the addition of different EO combinations evaluated as compared to control except PO+ CLO (1:1). At dose level (D2 and D3) GO+PO combination led to a moderate decrease in the in IVDMD and IVOMD along with decrease in in vitro methane production. Fraction of propionic acid was higher on addition of garlic and peppermint oil together. There was relative decrease in the methanogens population with bacteria as housekeeping gene as expressed by RT-PCR amplification with GO+PO addition. Present study concluded that among the EOs combinations in vitro tested, garlic and peppermint oil combination (GO+PO) has better potential in reducing in vitro methane production with lower effect on in vitro digestibility.