Abstract: [Objective] To assess the effect of extruded straw microbial fermented feed on ruminal fermentation of Dorper × Thin-tailed Han crossbred sheep using roughage as single factor variable. [Method] A total of 81 3-month-old Dorper × Thin-tailed Han crossbred lambs weighed （23±1.0） kg were selected, and were randomly divided into control group （70% concentrate + 30% dry straw）, experimental group Ⅰ （70% concentrate + 30% extruded straw microbial fermented feed） and experimental group Ⅱ （70% concentrate + 30% extruded straw microbial fermented feed, and then adding extruded sustained release urea accounting for 10% of dietary total protein concentration, NPN≥100%). There were 3 replicates for each group and 9 crossbred lambs for each replicate. The experimental period lasted for 75 days, including 15 days of pre-feeding and 60 days of formal feeding. [Result] The concentrations of ammoniacal nitrogen （NH₃-N） and bacterial protein （BCP） in experimental group Ⅱ were significantly （P<0.05） higher than those in experimental group Ⅰ and control group, while there was no significant （P>0.05） difference between experimental group Ⅰ and control group. No significant （P>0.05） inter-group differences in volatile fatty acid （VFA） associated indicators were observed in paired comparisons. [Conclusion] The extruded straw microbial fermented feed + NPN have a promoting effect on ruminal fermentation.

Key words: extruded straw microbial fermented feed, Dorper × Thin-tailed Han crossbred sheep;, ammoniacal nitrogen, bacterial protein, volatile fatty acid