Impact of Tannin Supplementation on Proteolysis during Post-Ruminal Digestion in Wethers Using a Dynamic In Vitro System: A Plant (Medicago sativa) Digestomic Approach.

The aim of this study was to characterize the effects of tannins on plant protein during sheep digestion using a digestomic approach combining in vivo (rumen) conditions and an in vitro digestive system (abomasum and small intestine). Ruminal fluid from wethers infused with a tannin solution or water (control) was introduced into the digester, and protein degradation was followed by liquid chromatography-tandem mass spectrometry (LC-MS/MS). Tannin infusion in the rumen led to a clear decrease in protein degradation-related fermentation end-products, whereas ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCo) protein was more abundant than in control wethers. In the simulated abomasum, peptidomic analysis showed more degradation products of RuBisCo in the presence of tannins. The effect of RuBisCo protection by tannins continued to impact Rubisco digestion into early-stage intestinal digestion but was no longer detectable in late-stage intestinal digestion. The peptidomics approach proved a potent tool for identifying and quantifying the type of protein hydrolyzed throughout the gastrointestinal tract.

Changes in the Rumen Microbiota of Cows in Response to Dietary Supplementation with Nitrate, Linseed, and Saponin Alone or in Combination.

Dietary supplementation with linseed, saponins, and nitrate is a promising methane mitigation strategy in ruminant production. Here, we aimed to assess the effects of these additives on the rumen microbiota in order to understand underlying microbial mechanisms of methane abatement. Two 2-by-2 factorial design studies were conducted simultaneously, which also allowed us to make a broad-based assessment of microbial responses. Eight nonlactating cows were fed diets supplemented with linseed or saponin in order to decrease hydrogen production and nitrate to affect hydrogen consumption; also, combinations of linseed plus nitrate or saponin plus nitrate were used to explore the interaction between dietary treatments. Previous work assessed effects on methane and fermentation patterns. Rumen microbes were studied by sequencing 18S and 16S rRNA genes and ITS1 amplicons. Methanogen activity was monitored by following changes in mcrA transcript abundance. Nitrate fed alone or in combination in both studies dramatically affected the composition and structure of rumen microbiota, although impacts were more evident in one of the studies. Linseed moderately modified only bacterial community structure. Indicator operational taxonomic unit (OTU) analysis revealed that both linseed and nitrate reduced the relative abundance of hydrogen-producing Ruminococcaceae Linseed increased the proportion of bacteria known to reduce succinate to propionate, whereas nitrate supplementation increased nitrate-reducing bacteria and decreased the metabolic activity of rumen methanogens. Saponins had no effect on the microbiota. Inconsistency found between the two studies with nitrate supplementation could be explained by changes in microbial ecosystem functioning rather than changes in microbial community structure.IMPORTANCE This study aimed at identifying the microbial mechanisms of enteric methane mitigation when linseed, nitrate, and saponins were fed to nonlactating cows alone or in a combination. Hydrogen is a limiting factor in rumen methanogenesis. We hypothesized that linseed and saponins would affect hydrogen producers and nitrate would affect hydrogen consumption, leading to reduced methane production in the rumen. Contrary to what was predicted, both linseed and nitrate had a deleterious effect on hydrogen producers; linseed also redirected hydrogen consumption toward propionate production, whereas nitrate stimulated the growth of nitrate-reducing and, hence, hydrogen-consuming bacterial taxa. This novel knowledge of microbial mechanisms involved in rumen methanogenesis provides insights for the development and optimization of methane mitigation strategies.

Rumen microbial and fermentation characteristics are affected differently by bacterial probiotic supplementation during induced lactic and subacute acidosis in sheep.

BACKGROUND: Ruminal disbiosis induced by feeding is the cause of ruminal acidosis, a digestive disorder prevalent in high-producing ruminants. Because probiotic microorganisms can modulate the gastrointestinal microbiota, propionibacteria- and lactobacilli-based probiotics were tested for their effectiveness in preventing different forms of acidosis. RESULTS: Lactic acidosis, butyric and propionic subacute ruminal acidosis (SARA) were induced by feed chalenges in three groups of four wethers intraruminally dosed with wheat, corn or beet pulp. In each group, wethers were either not supplemented (C) or supplemented with Propionibacterium P63 alone (P) or combined with L. plantarum (Lp + P) or L. rhamnosus (Lr + P). Compared with C, all the probiotics stimulated lactobacilli proliferation, which reached up to 25% of total bacteria during wheat-induced lactic acidosis. This induced a large increase in lactate concentration, which decreased ruminal pH. During the corn-induced butyric SARA, Lp + P decreased Prevotella spp. proportion with a concomitant decrease in microbial amylase activity and total volatile fatty acids concentration, and an increase in xylanase activity and pH. Relative to the beet pulp-induced propionic SARA, P and Lr + P improved ruminal pH without affecting the microbial or fermentation characteristics. Regardless of acidosis type, denaturing gradient gel electrophoresis revealed that probiotic supplementations modified the bacterial community structure. CONCLUSION: This work showed that the effectiveness of the bacterial probiotics tested depended on the acidosis type. Although these probiotics were ineffective in lactic acidosis because of a deeply disturbed rumen microbiota, some of the probiotics tested may be useful to minimize the occurrence of butyric and propionic SARA in sheep. However, their modes of action need to be further investigated.