Effects of dietary carbohydrate composition on rumen fermentation characteristics and microbial population in vitro

The objective of the experiment was to evaluate the effects of dietary carbohydrate composition on rumen fermentation characteristics and microbial populations <em>in vitro</em>. The treatments were organized in three different carbohydrate composition diets: the wheat fibre rich diet (WF) (67.2% wheat bran and 25.7% corn grain in concentration), mixed diet (MD) (45.1% wheat bran and 34.3% corn grain) and corn starch rich diet (CS) (2.1% wheat bran and 63.8% corn grain), respectively (n=6). The results showed that consumption of CS diet led to a decrease in NH3-N (ammonia nitrogen) concentration (P&lt;0.05), and microbial protein concentration were increased (P&lt;0.05). They indicated more efficient ruminal NH3-N utilization and microbial protein (MCP) synthesis with increasing corn starch proportion. Compared with WF diet, concentrations of acetate, propionate and TVFA (total volatile fat acid) were increased in MD and CS diets (P&lt;0.01). The results of Real-time PCR technique indicted that the microbes in rumen were sensitive to dietary carbohydrate composition, and the consumption of CS diets increased <em>Protozoa</em> population, as well as <em>Streptococcus</em> <em>bovis</em> (P&lt;0.05). <em>Butyrivibrio</em> <em>fibrisolvens</em> population of WF and MD (8 h) was higher than that of CS (P&lt;0.01), while <em>Butyrivibrio</em> <em>fibrisolvens</em> population (24 h) got lower within WF treatment (P&lt;0.01). These results indicated that the microbial community structure and improved ruminal fermentation are affected by the composition of dietary carbohydrate. Maximizing nitrogen utilization and MCP synthesis could be obtained when non-structural carbohydrate rich diet (2.1% wheat bran and 63.8% corn grain) was used.