Polyphenol-rich by-products to modulate the activity of rumen microbiota.

The rumen is the largest stomach in ruminants and hosts a complex microbial community which main role is to degrade the fibers ingested by the animal. Sugars derived from fibers degradation are then fermented to volatile fatty acids (the primary energy source for the animal), CO2 and CH4. Despite a core rumen microbiome exists, the composition of the microbial community in the rumen can be influenced by several factors, such as diet. Polyphenols are plant metabolites with a phenolic group that can be present in ruminants’ feed, or that can be added to the feed (e.g., by inclusion of agro-industrial by-products). Polyphenols can modulate the microbial activity by decreasing enteric CH4 production, with a positive impact on the environmental sustainability of animal productions. Furthermore, the presence of polyphenols in ruminants’ diet can modulate the fatty acids (FAs) biohydrogenation (i.e., the progressive isomerization and saturation of dietary fatty acids in the rumen), a microbiological process that influences the FAs profile and consequently the quality of animal products. Despite the effect of polyphenols on rumen microbiome is different according to animal species, polyphenol source and level of inclusion in the diet, there is general evidence that the content of saturated FAs decreases by feeding polyphenol-rich diets, while the content of conjugated linoleic acid isomers (i.e., FAs that can improve nutritional value) increases. The inclusion of polyphenol-rich by-products in ruminants’ diet is thus a valuable strategy to improve the quality of animal products and to decrease the environmental impact of livestock productions.