Abstract: [Objective] To investigate the effects of different levels of grape seed pomace （GSP） replacing partial corn and cottonseed meal in concentrate supplements on in vitro rumen gas production, in vitro nutrients digestibility, fermentation parameters, and growth performance of Simmental cattle. [Method] Using the rumen simulation technique, corn and cottonseed meal in concentrate supplements were partially replaced by GSP at proportions of 4%, 8%, 12% and 16%, respectively. The in vitro gas production, fermentation parameters, in vitro nutrients digestibility of each groups were measured, and the growth performance of the cattle fed with diets in which corn and cottonseed meal were partially replaced by different levels of GSP were evaluated. [Result] The cumulative gas production increased as the in vitro fermentation period extended. The 12% GSP group produced the most gas, and there was no significant （P>0.05） difference in total gas production across the different groups at 72 h of fermentation. There were no significant （P>0.05) differences in pH value, NH₃-N concentration, or bacterial protein content in the artificial rumen fluid between the different groups after gas production. The concentrations of volatile fatty acids increased significantly （P<0.05) in the experimental groups. The digestibility of dry matter was the lowest in the 16% GSP group. The digestibility of crude protein in the control group was significantly （P<0.05) higher than that in the experimental groups. The digestibility of neutral detergent fiber in the control group and the 4% GSP group was significantly （P<0.05) higher than that in the other three groups. The digestibility of acid detergent fiber in the control group and the 12% GSP group was significantly （P<0.05) higher than that in the other three groups. The average daily gain of the cattle in the 4% and the 8% GSP groups was 170 g/d and 140 g/d higher than that of the control group, respectively. [Conclusion] Replacement of partial corn and cottonseed meal in concentrate supplements with GSP improved the concentrations of volatile fatty acids in artificial rumen fluid. Replacing proportions of 4% or 8% of GSP increased the daily gain and boosted the rumen fermentation of beef cattle, which was conducive to improve the growth performance.

Key words: Simmental cattle, grape seed pomace, in vitro rumen fermentation, digestibility, growth performance