Abstract: In this study, in vitro gas production technique was used to investigate the effect of different levels of disodium fumarate on rumen fermentation in sheep with a one-factor completely randomized design. The soluble starch and cellulose were used as carbon sources, tryptone was used as nitrogen source. Disodium fumarate accounting for 1.0%, 2.0% and 3.0% of the dry matter of fermentation substrate were added in experimental groups 1, 2 and 3, respectively. The control group received no addition of disodium fumarate. The results showed that compared with the control group, adding 1% of disodium fumarate （experimental group 1） could significantly （P<0.05） improve the output of total volatile fatty acids, acetic acid, propionic acid and butyric acid, in vitro gas production, and dry matter degradation rate; the significantly （P<0.05） increased output of total volatile fatty acids, acetic acid, propionic acid and butyric acid as well as significantly （P<0.05） elevated dry matter degradation rate were observed in experimental group 2 compared to the control group; there was no significant （P>0.05） differences in ammonia nitrogen concentration, total volatile fatty acid and acetic acid output, gas production and dry matter degradation rate between experimental group 3 and control group, but experimental group 3 had significantly （P<0.05） increased propionic acid production. In conclusion, adding 1% or 2% fumarate disodium can significantly improve the rumen fermentation performance of sheep, but adding 3% fumarate disodium exhibited an inhibiting effect on rumen fermentation capacity to a certain extent.

Key words: in vitro gas production technique, fumarate disodium, fermentation parameters, gas production, dry matter degradation rate, sheep