Abstract: Four Simmental steers(average BW 420 kg, aged 2.5) with permanent rumen cannula and consuming a corn straw diet were used in a 4×4 Latin square design and supplemented with four levels(0, 0.02, 0.04 and 0.06g/kgW) of supplemental isovalerate to evaluate the effects of isovalerate on ruminal pH, NH3-N, and VFA. The results showed that ruminal pH of supplemental isovalerate 0.06 g/kgW decreased (P<0.05). The NH3-N concentrations of 0.04 g/kgW and 0.06 g/kgW group were lower than control and 0.02 g/kgW group significantly (P<0.05). Ruminal actate, butyrate, acetate/propionate, TVFA, and purine derivatives of urine were increased significantly (P<0.05) by isovalerate supplementation with 0.04 g/kgW. The supplementation of isovalerate had passive effect on rumen fermentation, the optimum dose was 0.04g/kgW.

Key words: simmental steer; isovalerate; rumen fermentation