Forage type and fish oil cause shifts in rumen bacterial diversity

Despite evidence supporting improved incorporation of beneficial polyunsaturated fatty acids (PUFA) into ruminant products, such as meat and milk, following red clover and fish oil (FO) inclusion in the ruminant diet, little is known regarding the concomitant bacterial diversity. We evaluated the effects of feeding grass vs. red clover silage with incremental FO inclusion on known lipolytic, biohydrogenating, cellulolytic and proteolytic rumen bacterial communities of steers. Following 14 days of dietary adaptation, liquid-associated (LAB) and solid-associated (SAB) bacterial communities were harvested, DNA extracted and bacterial denaturing gradient gel electrophoresis (DGGE) and specific-bacterial quantitative PCR (QPCR) were undertaken. DGGE-derived dendrograms showed that diet caused the greatest change in LAB and SAB bacterial diversity, with FO inclusion at the 2% and 3% dry matter intake also causing some changes. QPCR revealed that diet resulted in changes in the DNA concentration of Anaerovibrio lipolytica, the Butyrivibrio proteoclasticus group, Fibrobacter succinogenes, Ruminococcus albus and Ruminococcus flavefaciens. FO inclusion caused changes in A. lipolytica, F. succinogenes and R. flavefaciens DNA concentration only. In the B. proteoclasticus group, which are the only known bacteria with the capacity to biohydrogenate PUFA to 18:0, DNA concentration did not correlate to 18:0 flow to the duodenum, however, suggesting that other bacteria may play a role in biohydrogenation. A greater understanding of microbial changes that accompany beneficial dietary changes will lead to novel strategies to improve ruminant product quality.