Abstract：This study was conducted to determine the effects of supplementing different level of malic acid (MA) and unsaturated fat acid, including oleic acid (OA), linoleic acid (LA) and linolenic acid (LNA) on rumen fermentation and functional microbe in vitro. The result showed the concentration of propionate acid was significantly increased (P<0.01), total gas and CH4 gas production were obviously decreased, and other VFA were significantly decreased accompanied with increased unsaturation of fatty acid; Methanobactrium formicicum in LA and LNA was obviously increased （P<0.01）, Ruminococcus flavefaciens and Ruminococcus albus were significant increased (P<0.01) compared with CK. However, Anaerovibrio lipolytica and Butyrivibrio fibrisolve were decreased (P<0.05) than CK. Methanobactrium formicicum in 10 mmol/L MA-OA which was decreased obviously (P<0.05). The conclusion was unsaturated fatty acid and malic acid could effectively change rumen fermentation profile but there were no directly relationship between them to inhibit CH4 production, and no obviously effect of supplementing malic acid and unsaturated fat acid on main rumen microbe.
