Effects of Phlorotannins from Sargassum on In Vitro Rumen Fermentation, Microbiota and Fatty Acid Profile

SIMPLE SUMMARY: The use of plant bioactive compounds like tannins to modulate ruminal biohydrogenation is a good strategy to optimize the fatty acid composition of ruminant-derived products, which are closely associated with human health. Differently from terrestrial tannins, there is little information on the effect of phlorotannins (PTs) from brown seaweeds on ruminal biohydrogenation. Thus, this study aimed to evaluate the effect of PT extract from Sargassum on in vitro rumen fermentation, fatty acid composition and bacterial community. The inclusion of PT extract had a positive effect on rumen fermentation by increasing dry matter digestibility and gas production and reducing ammonia-N concentration. Rumen biohydrogenation was profoundly inhibited by PTs as reflected in an increased unsaturated fatty acid and reduced saturated fatty acid production. The addition of PTs also changed the rumen bacterial community significantly with elevated carbohydrate-mediated bacteria. Correlation analysis found that Prevotellaceae_UCG-001, Anaerovorax, Ruminococcus, Ruminobacter, Fibrobacter, Lachnospiraceae_AC2044_group and Clostridia_UCG-014 might be involved in the biohydrogenation process. The results suggest that the inclusion of PTs in the diet improved rumen fermentation and fatty acid composition through modulating rumen microbiota. ABSTRACT: The fatty acid profiles of ruminant-derived products are closely associated with human health. Ruminal microbiota play a vital role in modulating rumen biohydrogenation (BH). The aim of this study was to assess the influence of dietary supplementation with phlorotannins (PTs) extracted from Sargassum on rumen fermentation, fatty acid composition and bacterial communities by an in vitro culture study. The inclusion of PTs in the diet increased dry matter digestibility and gas production, and reduced ammonia-N concentration and pH. PT extract inhibited rumen BH, increasing the content of trans-9 C18:1, cis-9 C18:1, trans-9 and trans-12 C18:2 and reducing C18:0 concentration. 16S rRNA sequencing revealed that PTs caused an obvious change in rumen bacterial communities. The presence of Prevotella decreased while carbohydrate-utilizing bacteria such as Prevotellaceae_UCG-001, Ruminococcus, Selenomonas, Ruminobacter and Fibrobacter increased. Correlation analysis between rumen FA composition and the bacterial microbiome revealed that Prevotellaceae_UCG-001, Anaerovorax, Ruminococcus, Ruminobacter, Fibrobacter, Lachnospiraceae_AC2044_group and Clostridia_UCG-014 might have been involved in the BH process. In conclusion, the results suggest that the inclusion of PTs in the diet improved rumen fermentation and FA composition through modulating the rumen bacterial community.