Addition of tannins to starch-rich diet stabilizes ruminal microbiota in bovines

Many reports suggest inclusion of polyphenol-rich plant extracts in feed improve performance and health in ruminants. Although these effects have been attributed to protein bypass of ruminal digestion, this mechanism cannot entirely explain the growth-promoting effect. Bovine rumen houses a complex microbiota able to convert indigestible plant mass into energy, which can be modulated by tannins. High-throughput sequencing of 16S rRNA gene (Illumina MiSeq platform) was used to study the temporal changes in rumen composition of six steers before and after addition of chestnut and quebracho tannins to diet. A total of 9.871.395 reads of 16S V3 region were obtained. Total number of phyla increased from 34 to 40 after tannins addition to diet. Moreover, Shannon’s diversity index increased significantly through time (p<0.05), concomitantly with a 5-fold reduction in its standard deviation, which shows that rumen microbiota acquired a higher complexity and was progressively stabilized after tannin treatment. Firmicutes correlated directly with time (R=0.95) and inversely with non-protein nitrogen levels (R=0.91). Moreover, a significant increase in the Firmicutes/Bacteroidetes ratio was observed over time from 0.77 to 1.10 (p<0.05), which has been shown to affect energy harvesting and fat production in different hosts. Ruminal tannins affected possitively the microbiome balance.