Bacterial diversity between solid and liquid fractions of rumen digesta from Korean native black goat, Hanwoo cattle, and Holstein Friesian cattle

We aimed to compare the rumen micro- bial diversity among 3 growing ruminants (Korean native black goats, Korean native Hanwoo cattle, and Holstein Friesian cattle) under the same feeding conditions and to investigate host-specific preferences of ruminal bacteria. Korean native black goats (14 mo, 55 ± 4.5 kg), Korean native Hanwoo cattle (20 mo, 550 ± 47 kg), and exotic Holstein Friesian cattle (24 mo, 645 ± 45 kg) were selected for the experiment. Ex- perimental ruminants were fed ad libitum twice daily at 0900 and 1800 h with a mixture of concentrate and Italian ryegrass (4:6 ratio) for more than 2 wk. The fermentation characteristics and bacterial diversity in solid and liquid fractions of rumen digesta were analyzed. Korean black goats had the lowest pH (6.50) and the greatest total VFA concentra- tion (134.93 mmol/L) and A/P ratio (4.55) among the 3 species. In addition, we found 15 bacterial phyla in rumen solid and liquid fractions from the 3 species using 16S rRNA gene sequencing. Furthermore, we identified differ- entially distributed bacteria among the ruminants, with 10 phyla showing significance for at least one of the rumi- nant species either in the rumen solid or liquid fraction. The bacterial community of Hanwoo cattle was similar to that of Holstein cattle but unlike that of goats. However, 6 bacterial species had a negative correlation of more than −0.7 between Hanwoo and Holstein cattle, suggesting an altered microbial ecosystem either in solid or liquid frac- tions. Moreover, several bacterial species from the goat rumen showed a distinct correlation between Hanwoo and Holstein cattle. A large proportion of Bacteroidetes and Firmicutes was found in liquid and in solid fractions, re- spectively. Overall, the results suggested host-specific preferences of bacteria for rumen function and their species-specific growth preference in the rumen of different ruminants. These findings could contribute to our understanding of the rumen microbial ecosystem for improving the rumen activity and health of cattle and goat species.