title: Redirection of Metabolic Hydrogen by Inhibiting Methanogenesis in the Rumen Simulation Technique (RUSITEC).
abstract: A decrease in methanogenesis is expected to improve ruminant performance by allocating rumen metabolic hydrogen ([2H]) to more energy-rendering fermentation pathways for the animal. However, decreases in methane (CH4) emissions of up to 30% are not always linked with greater performance. Therefore, the aim of this study was to understand the fate of [2H] when CH4production in the rumen is inhibited by known methanogenesis inhibitors (nitrate, NIT; 3-nitrooxypropanol, NOP; anthraquinone, AQ) in comparison with a control treatment (CON) with the Rumen Simulation Technique (RUSITEC). Measurements started after 1 week adaptation. Substrate disappearance was not modified by methanogenesis inhibitors. Nitrate mostly seemed to decrease [2H] availability by acting as an electron acceptor competing with methanogenesis. As a consequence, NIT decreased CH4production (-75%), dissolved dihydrogen (H2) concentration (-30%) and the percentages of reduced volatile fatty acids (butyrate, isobutyrate, valerate, isovalerate, caproate and heptanoate) except propionate, but increased acetate molar percentage, ethanol concentration and the efficiency of microbial nitrogen synthesis (+14%) without affecting gaseous H2. Nitrooxypropanol decreased methanogenesis (-75%) while increasing both gaseous and dissolved H2concentrations (+81% and +24%, respectively). Moreover, NOP decreased acetate and isovalerate molar percentages and increased butyrate, valerate, caproate and heptanoate molar percentages as well as n-propanol and ammonium concentrations. Methanogenesis inhibition with AQ (-26%) was associated with higher gaseous H2production (+70%) but lower dissolved H2concentration (-76%), evidencing a lack of relationship between the two H2forms. Anthraquinone increased ammonium concentration, caproate and heptanoate molar percentages but decreased acetate and isobutyrate molar percentages, total microbial nitrogen production and efficiency of microbial protein synthesis (-16%). Overall, NOP and AQ increased the amount of reduced volatile fatty acids, but part of [2H] spared from methanogenesis was lost as gaseous H2. Finally, [2H] recovery was similar among CON, NOP and AQ but was largely lower than 100%. Consequently, further studies are required to discover other so far unidentified [2H] sinks for a better understanding of the metabolic pathways involved in [2H] production and utilization.
authors.affiliation: Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada Lethbridge, AB, Canada.
authors.forename: Jessie
authors.initials: J
authors.lastname: Guyader
authors.affiliation: Instituto de Investigaciones Agropecuarias INIA Carillanca Temuco, Chile.
authors.forename: Emilio M
authors.initials: EM
authors.lastname: Ungerfeld
authors.affiliation: Lethbridge Research and Development Centre, Agriculture and Agri-Food Canada Lethbridge, AB, Canada.
authors.forename: Karen A
authors.initials: KA
authors.lastname: Beauchemin
keywords: fermentation; hydrogen; in vitro; methane; microbial biomass; reduced product; volatile fatty acid