Melaleuca erecifolia essential oil (MEEO) and its main compound D-linalool (DL) have been found to inhibit methane production by rumen microbes in the in vitro batch system. However, the persistency of this effect, or the impact on overall microbial fermentation over time are unknown. The objective of the present study was to investigate the effect of MEEO and DL on in vitro methane production and fermentation in the rumen-simulating continuous culture system (RUSITEC). Experimental treatments were control (a concentrate-based diet), and MEEO or DL, included at 12.5 µl/g control substrate. The experimental period consisted of 19 days, with 12 days of treatment and measurements. Microbial gas and methane production were measured daily, while other fermentation products such as volatile fatty acids (VFA) and NH3 from fermentation liquid, as well as feed digestibility (dry matter disappearance, DMD) from feed residue were analyzed on day 8, 15 and 19. Overall, when compared to control, methane production (ml/24 h) was significantly (P<0.05) reduced by addition of MEEO (by 10.4%) and DL (by 17.6%). However, this was accompanied with a significant reduction in gas production (14.7% and 24.4 %), DMD (3.6 and 7.1%) and NH3 (36 and 21.8 %), but the VFA concentrations were reduced with DL addition only (by 17%). These effects of MEEO and DL on methane and fermentation were persistent across the sampling days. The study confirmed that in an open fermentation system and at a dose tested here, MEEO and DL can persistently reduce methane over time, but can have some negative effect on microbial fermentation. While MEEO and DL have potential to reduce ruminal methane, an optimal dose for this is yet to be established. Acknowledgement: This work was funded by MLA NLMP program
