Abstract: [Objective] To assess the effects of different levels of dried apple pomace （DAP） replacing part of the energy feed in concentrate supplements on in vitro rumen gas production, fermentation parameters, nutrients digestibility and growth performance of fattening Simmental cattle. [Method] Corns in concentrate supplements were partially replaced by DAP at proportions of 0, 4%, 8%, 12% and 16%, respectively. The rumen gas production of each group during 0 to 72 h of fermentation was monitored by using in vitro gas production method, and the fermentation parameters of the artificial rumen fluid were determined at the end of the in vitro gas production test. The nutrients digestibility of the artificial rumen fluid was measured at 48 h of in vitro fermentation. The weight gain indicators of the fattening cattle fed with diets in which corns were partially replaced by DAP at proportions of 4%, 8%, 12% and 16%, respectively, were assessed. [Result] The 4% DAP replacing group had significantly （P<0.05） higher total gas production in comparison to 8% and 16% DAP replacing groups. The gas production of each group was mainly observed in 4 to 24 h of fermentation and tended to be stable during 36 to 72 h of fermentation. After gas production, the pH value of the artificial rumen fluid of each group was in the normal range. The concentration of ammonia nitrogen （NH₃-N） of 8% DAP replacing group was significantly （P<0.05） higher than that of 12% and 16% DAP replacing groups. The concentrations of acetic acid, isobutyric acid, butyric acid, isovaleric acid, and valeric acid of 4% and 8% DAP replacing groups were significantly （P<0.05） higher than those of the remaining groups. The control group had significantly （P<0.05） higher digestibility of dry matter （DM）, crude protein （CP） and neutral detergent fiber （NDF） compared with the remaining groups, and 8% DAP replacing group had significantly （P<0.05） higher digestibility of acid detergent fiber （ADF） compared with the remaining groups. There were no significant （P>0.05） differences in total weight gain and daily weight gain during the test period among the fattening cattle in different groups. [Conclusion] Replacement of partial corns in concentrate supplements with 4% DAP increased the rumen gas production in in vitro fermentation of fattening Simmental cattle. 4% and 8% DAP replacements increased the concentrations of NH₃-N and volatile fatty acid （VFA） in rumen fluid, which was beneficial to rumen fermentation and diet digestion.

Key words: dried apple pomace, concentrate supplements, in vitro fermentation, growth performance