Abstract:

The purpose of this study was to investigate the effects of red clover extract on rumen microbial composition and urea metabolism in vitro. The experiment was divided into control group (no red clover extract added) and supplement with red clover extract treatment group. Rumen fluid collected from 3 healthy cows were mixed for in vitro fermentation. The fermentation fluid samples were collected at 0, 0.5, 1, 2, 4, 6 and 24 h of fermentation, respectively, and the contents of urea, ammonia nitrogen (NH₃-N), microbial crude protein and total amino acids were determined. 16S rRNA sequencing was used to reveal the changes of microbial diversity, community composition and function in rumen. The results showed that in the red clover extract treatment group, urea decomposition rate was significantly reduced within 4 h of fermentation, ammonia nitrogen content was significantly reduced after 2 h of fermentation, rumen microbial protein content was significantly increased after 6 h of fermentation, and total free amino acid content was not significantly affected. 16S rRNA sequencing results showed that supplemented with red clover extract significantly increased the Chao 1 and Shannon indexes of microbial α diversity and changed the rumen microbial community structure in the in vitro fermentation. The abundance of Prevotella (ASV 35 and s_unidentified_rumen_bacterium_RF18) and Ruminobacter were changed, Bilophil were decreased. In summary, the addition of red clover extract can reduce the rate of urea hydrolyzing by rumen bacteria, and improving the ability of rumen bacteria to convert ammonia nitrogen into microbial crude protein.

Key words: red clover extract, rumen, urea, bacterial diversity