Effects of two lipids on in vitro ruminal methane production

The effects on mixed ruminal cultures of olive oil (OO) and a hexadecatrienoic acid (HA, cis-C16:6,9,12) extracted from the Hawaiian algae Chaetoceros were studied in 24 h-batch fermentation. HA at 0.5, 1 and 2 ml/l linearly decreased CH4 production by 25, 47 and 97%, respectively, while OO did not affect it. HA at 0.5, 1 and 2 ml/l increased H2 accumulation by 2-, 2- and 5-fold, respectively. Release of CO2 was linearly decreased by HA at 0.5, 1 and 2 ml/l by 10, 32 and 48%, respectively, while OO linearly increased it by 9, 2 and 17%, at the same concentrations. Apparently fermented OM, as estimated through the VFA production stoichiometry, was linearly decreased by HA at 0.5, 1 and 2 ml/l by 9, 19 and 42%, respectively, while OO did not affect it. HA decreased acetate molar percentage, increased propionate, and tended to decrease butyrate. OO tended to decrease acetate molar percentage, and increased propionate and butyrate molar percentages. HA at 0.5, 1 and 2 ml/l linearly decreased NH4+ concentration by 5, 5 and 21%, respectively. HA was a strong inhibitor of methanogenesis, but decreased fermentation and increased H2 accumulation. Addition of OO increased propionate production and did not seem to inhibit fermentation.