This CH4 suppressing effect may relate to the degree of unsaturation of these FA as they undergo biohydrogenation in the rumen, their reactivity in the rumen, and their effects on specific rumen microorganisms (e.g., cellulolytic bacteria and protozoa). Although interesting, to the best of our knowledge, the existing experimental data on the effects of specific long-chain PUFA of FO on CH4 emission are scarce. The few studies involved are primarily based on in vitro procedures (e.g., Fievez et al., 2003; Patra and Yu, 2013) or on in vivo studies conducted at pasture (Woodward et al., 2006). Particularly, Woodward et al. (2006) showed a positive effect of FO on reducing CH4emissions in a short-term study, whereas no reduction was observed for a longer-term study.