Use of essential oils in combination with fibrolytic enzymes to decrease in vitro ruminal methane production

Exogenous enzymes and essential oils (EOs) have both improved fibre digestion in ruminants, but the effect on ruminal fermentation and methane emission of combining these additives requires further evaluation. Various EOs were used in combination with an enzyme in an in vitro gas production system to measure organic matter digestibility and methane after 48 hours of incubation of Eragrostis curvula. The treatments consisted of T1) unaugmented control; T2) enzyme (cellulose-xylanase mixture, 1:1 w/w, 1.5 mL/g DM); T3) enzyme combined with Next Enhance® (cinnamaldehyde with diallyl disulfide and diallyl trisulfide, 43:3.85 w/wt); T4) enzyme and cinnamon oil; T5) enzyme and garlic oil; and T6) enzyme with cinnamon and garlic oil, 1:1 w/w). At 2, 4, 8, 12, 24, 36, and 48 hours of incubation, gas production was measured, and gas samples were analysed for methane concentration. The inclusion of additives affected cumulative gas production (P <0.05), but only slightly affected methane production (P =0.05) after 48 hours of incubation. The addition of enzymes increased both gas and methane production. T5 and T6 both reduced gas production compared with T2. Combining EOs with an enzyme reduced methane production compared with T2 after 48 hours of incubation. The additives tended to increase in vitro organic matter digestibility (P =0.09), although they showed a tendency towards reduced methane production per unit of organic matter digested (P =0.07). Further studies on these enzyme and EO combinations under different doses and substrates are required to validate their efficacy for ruminant production. Keywords: cinnamon oil, cinnamaldehyde, garlic oil, gas production, glucanase, in vitro digestibility, xylanas