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.

OBJECTIVES: 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. METHODS: 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. RESULTS: 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. CONCLUSIONS: 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.

Winery by-products as a feed source with functional properties: dose-response effect of grape pomace, grape seed meal, and grape seed extract on rumen microbial community and their fermentation activity in RUSITEC.

BACKGROUND: Grape and winery by-products have nutritional values for cattle and also contain functional compounds like phenols, which not only bind to protein but can also directly affect microbiota and their function in the rumen. We characterized the nutritional and functional effects of grape seed meal and grape pomace as well as an effective dosage of grape phenols on ruminal microbiota and fermentation characteristics using a rumen simulation technique. RESULTS: Six diets (each n = 8) were compared including a control diet (CON, no by-product), a positive control diet (EXT, CON + 3.7% grape seed extract on a dry matter (DM) basis), two diets with grape seed meal at 5% (GS-low) and 10% (GS-high), and two diets with grape pomace: at 10% (GP-low) and 20% (GP-high), on a DM basis. The inclusion of the by-product supplied total phenols at 3.4%, 0.7%, 1.4%, 1.3%, and 2.7% of diet DM for EXT, GS-low, GS-high, GP-low, and GP-high, respectively. Diets were tested in four experimental runs. All treatments decreased ammonia concentrations and the disappearances of DM and OM (P < 0.05) compared to CON. EXT and GP-high lowered butyrate and odd- and branch-chain short-chain fatty acids while increased acetate compared to CON (P < 0.05). Treatments did not affect methane formation. EXT decreased the abundance of many bacterial genera including those belonging to the core microbiota. GP-high and EXT consistently decreased Olsenella and Anaerotipes while increased Ruminobacter abundances. CONCLUSION: The data suggest that the inclusion of winery by-products or grape seed extract could be an option for reducing excessive ammonia production. Exposure to grape phenols at a high dosage in an extract form can alter the rumen microbial community. This, however, does not necessarily alter the effect of grape phenols on the microbial community function compared to feeding high levels of winery by-products. This suggests the dominant role of dosage over the form or source of the grape phenols in affecting ruminal microbial activity. In conclusion, supplementing grape phenols at about 3% of diet DM is an effective dosage tolerable to ruminal microbiota.