Rumen microbial responses to supplemental nitrate. II. Potential interactions with live yeast culture on the prokaryotic community and methanogenesis in continuous culture

Abstract

Nitrates have been fed to ruminants, including dairy cows, as an electron sink to mitigate CH 4 emissions. In the NO 3 − reduction process, NO 2 − can accumulate, which could directly inhibit methanogens and possibly other microbes in the rumen. Saccharomyces cerevisiae yeast was hypothesized to decrease NO 2 − through direct reduction or indirectly by stimulating the bacterium Selenomonas ruminantium, which is among the ruminal bacteria most well characterized to reduce both NO 3 − and NO 2 −. Ruminal fluid was incubated in continuous cultures fed diets without or with NaNO 3 (1.5% of diet dry matter; i.e., 1.09% NO 3 −) and without or with live yeast culture (LYC) fed at a recommended 0.010 g/d (scaled from cattle to fermentor intakes) in a 2 × 2 factorial arrangement of treatments. Treatments with LYC had increased NDF digestibility and acetate: propionate by increasing acetate molar proportion but tended to decrease total VFA production. The main effect of NO 3 − increased acetate: propionate by increasing acetate molar proportion; NO 3 − also decreased molar proportions of isobutyrate and butyrate. Both NO 3 − and LYC shifted bacterial community composition (based on relative sequence abundance of 16S rRNA genes). An interaction occurred such that NO 3 − decreased valerate molar proportion only when no LYC was added. Nitrate decreased daily CH 4 emissions by 29%. However, treatment × time interactions were present for both CH 4 and H 2 emission from the headspace; CH 4 was decreased by the main effect of NO 3 − until 6 h postfeeding, but NO 3 − and LYC decreased H 2 emission up to 4 h postfeeding. As expected, NO 3 − decreased methane emissions in continuous cultures; however, contrary to expectations, LYC did not attenuate NO 2 − accumulation.

Impact of Nutrients on the Hoof Health in Cattle

“…Yeast cultures in the feed ration do not affect the prevalence of lameness in cows, but have the effect of reducing the locomotion score [ 29 ]. Yeast culture, especially Saccharomyces cerevisiae, often improves digestibility of neutral detergent fiber [ 138 , 139 ] could increase acetate, but also increase the production of dry matter intake and milk. Yeast increases the availability of dicarboxylic acids, which perform central metabolic reactions and serve as electron carriers [ 138 ].…”

Potential roles of nitrate and live yeast culture in suppressing methane emission and influencing ruminal fermentation, digestibility, and milk production in lactating Jersey cows

“…Rather than strategies to inhibit H 2 production to suppress methanogenesis, alternative electron receptors such as NO 3 − salts have been added so that NO 3 − -reducing bacteria compete with methano-6145 gens for aqueous H 2 (Morgavi et al, 2010). Therefore, our aim was to assess whether dietary NO 3 − salts would mitigate methanogenesis while potentially shifting fermentation pathways and bacterial populations, as we detected in continuous culture (Welty et al, 2019).…”

“…Such variability might be a result of sequencing approaches compared with quantitative PCR (Jiang et al, 2017). However, protozoa and uncharacterized bacteria other than S. ruminantium appear to have important roles in NO 3 − and NO 2 − reduction (Yang et al, 2016), and protozoa appear to reduce NO 3 − but also are inhibited by NO 2 − (Roman-Garcia et al, 2019). In a previous study, Welty et al (2019) suggested that live yeast culture (LYC) could help mediate NO 2 − accumulation in continuous cultures.…”

“…However, protozoa and uncharacterized bacteria other than S. ruminantium appear to have important roles in NO 3 − and NO 2 − reduction (Yang et al, 2016), and protozoa appear to reduce NO 3 − but also are inhibited by NO 2 − (Roman-Garcia et al, 2019). In a previous study, Welty et al (2019) suggested that live yeast culture (LYC) could help mediate NO 2 − accumulation in continuous cultures. Therefore, the LYC Yea-Sacc Saccharomyces cerevisiae 1026 (Alltech Inc., Nicholasville, KY) was fed to lactating dairy cattle in the current study.…”

Soil Nitrogen Treatment Alters Microbiome Networks Across Farm Niches

“…Despite the growing interest of agricultural microbiomes and their responses to different agricultural management systems, the focus has been usually within speci c niches, such as soil [61,62], rumen [63,64], or rhizosphere [28,65]. However, microbial interactions also play a critical role in many ecosystem process, especially nutrient cycling [66], that may have carry over effects into other niches.…”