Evaluation of a single‐flow continuous culture fermenter system for determination of ruminal fermentation and enteric methane production

A 4‐unit, single‐flow continuous culture fermenter system was developed to assessin vitro nutrient digestibility, volatile fatty acid (VFA) concentration and daily entericmethane (CH4) production of ruminant diets. The objective was to develop a closed‐vessel system that maintained protozoal populations and provided accurate predic‐tions of total CH4 production. A diet of 50% orchardgrass (Dactylis glomerata L.) and50% alfalfa (Medicago sativa L.) was fed during 4, 10‐day periods (7‐day adaptationand 3‐day collection). Fermenters were fed 82 g of dry matter (DM)/day in four equalfeedings. pH and temperature were taken every 2 min, and CH4 concentration wasmeasured every 10 min. Samples for DM and protozoal counts were taken daily, anddaily effluent samples were collected for determination of DM, VFA and NH3‐N con‐centrations. There was no effect (p > 0.17) of adaptation versus collection days on ves‐sel and effluent DM, temperature or pH. Initial protozoal counts decreased (p < 0.01),but recovered to initial counts by the collection period. Total VFA, acetate, propionateand isobutyrate concentrations did not differ (p ≥ 0.13) among periods or days of thecollection period. There was no difference (p ≥ 0.37) among days or periods in totaldaily CH4 production and CH4 production per g of OM, NDF, digestible OM or digest‐ible NDF fed. Data collected throughout 4 experimental periods demonstrated thatthe system was able to reach a steady state in fermentation well within the 7‐dayadaptation period and even typically variable data (i.e., CH4 production) were stablewithin and across periods. While further research is needed to determine the relation‐ship between this system and in vivo data, this continuous culture fermenter systemprovides a valid comparison of in vitro ruminal fermentation and enteric CH4 produc‐tion of ruminant diets that can then be further validated with in vivo studies