Abstract: 【Objective】An experiment was conducted to determine the effect of thiamin on rumen fermentation and microbial community under different nitrogen levels to sulfur ratio in Rusitec. 【Method】 A 2×2 two factorial design of an experiment was adopted: one factor was different nitrogen levels to sulphur ratios (5﹕1, 15﹕1), the other was different substrates with and without adding thiamin (0 and 60 mg•kg-1). 【Result】 The results showed that there was no significant effect on pH and ammonia concentration in the substrates. The high sulfur level restrained the synthesis of bacterial protein and significantly decreased the ratio of protozoal protein and bacterial protein (P＜0.05). There was no effect on the concentrations of acetate, propionate and the acetate/propionate ratio (P＜0.05). The low sulfur level increased the concentration of butyrate, total VFAs and the proportion of butyrate, and the high S level reduced the total concentration of thiamin while the total thiamin was increased by adding thiamin. There was an obvious consequence that the high sulfur substrate declined the concentration of the lactate in Rusitec. Compared to the without adding thiamin group, the relative number of Strepococcus bovis in substrates with adding thiamin decreased by 5.90% (P＜0.05) and 2.05% (P＜0.01) under the same nitrogen/sulfur ratios, and there was no significant effect on the number of Butyrivibrio fibrisovens. 【Conclusion】 It was concluded that rumen fermentation was response to sulfur level in Rusitec, higher levels of sulfur in sulfur substrate could decline the concentration of the lactate and bacterial protein while protozal protein dropped in Rusitec. It was found that sulfur and thiamin play an important role in suppressing of subacute rumen acidosis (SARA). Adding thiamin in Rusitec resulted in the decrease of the relative number of S. bovis in substrates, but had no significant effect on the number of B. fibrisovens.

Key words: thiamin, rumen fermentation, rumen micro-organisms