Changes in the solid-associated bacterial and fungal communities following ruminal in vitro fermentation of winery by-products: aspects of the bioactive compounds and feed safety.

Feeding winery by-products (WBP) could affect the bovine microbiome because of their phenol compounds and a transfer of WBP-associated microbiota. This work examined changes in the underexplored solid-associated rumen microbiome following the inclusion of WBP. Using the rumen simulation technique, fermenters were inoculated with the inoculum of donor cows and were fed one of six dietary treatments including a control diet of 70 % hay +30 % concentrate (CON), control diet + 3.7 % commercial grapeseed extract (EXT), 65 % hay + 25 % concentrate + 10 % grape pomace (GP-low), 56 % hay + 24 % concentrate + 20 % grape pomace (GP-high), 70 % hay + 25 % concentrate + 5 % grapeseed meal (GS-low), and 65 % hay + 25 % concentrate + 10 % grapeseed meal (GS-high) (dry matter basis). The compositional changes of bacteria, archaea and fungi in the solid fractions were based on 16S and ITS2 rRNA sequencing. The alpha- and beta-diversity of the microbiota were unaffected. However, treatment modified the bacterial composition at low taxonomic levels. Butyrivibrio fibrisolvens , Treponema bryantii , and bacterium MC2010 decreased in EXT, while Treponema berlinense was increased in GP-high and GP-low compared to CON. Concerning fungi, GS-high increased Candida spp. , Lachancea spp. , Microdochium spp. , Mucor spp. , Pichia spp. , Saturnispora spp. , and Zygosaccharomyces spp. compared to CON. Many non- Saccharomyces yeasts were detected in WBP samples but absent in donor cows and CON samples. The genera affected by treatment were not the major contributors to the ruminal degradation of nutrients. The results indicate a sensitivity of rumen solid bacteria to grape phenols when delivered as an extract and a transfer of WBP-associated microbiota into the rumen. • Rumen bacteria and fungi were sensitive to grape phenols in an extract form. • Winery by-products introduced non- Saccharomyces yeasts into the rumen community. • Affected genera were not major contributors to the nutrient degradation. • Donor cows' microbiota data are essential when interpreting the in vitro effects. [ABSTRACT FROM AUTHOR]