A 4-unit, single-flow continuous culture fermenter system was developed to assess in vitro nutrient digestibility, volatile fatty acid (VFA) concentration and daily enteric methane (CH4 ) production of ruminant diets. The objective was to develop a closed-vessel system that maintained protozoal populations and provided accurate predictions of total CH4 production. A diet of 50% orchardgrass (Dactylis glomerata L.) and 50% alfalfa (Medicago sativa L.) was fed during 4, 10-day periods (7-day adaptation and 3-day collection). Fermenters were fed 82 g of dry matter (DM)/day in four equal feedings. pH and temperature were taken every 2 min, and CH4 concentration was measured every 10 min. Samples for DM and protozoal counts were taken daily, and daily effluent samples were collected for determination of DM, VFA and NH3 -N concentrations. There was no effect (p > 0.17) of adaptation versus collection days on vessel 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, propionate and isobutyrate concentrations did not differ (p ≥ 0.13) among periods or days of the collection period. There was no difference (p ≥ 0.37) among days or periods in total daily CH4 production and CH4 production per g of OM, NDF, digestible OM or digestible NDF fed. Data collected throughout 4 experimental periods demonstrated that the system was able to reach a steady state in fermentation well within the 7-day adaptation period and even typically variable data (i.e., CH4 production) were stable within and across periods. While further research is needed to determine the relationship between this system and in vivo data, this continuous culture fermenter system provides a valid comparison of in vitro ruminal fermentation and enteric CH4 production of ruminant diets that can then be further validated with in vivo studies.
Keywords: continuous culture; digestibility; methane; protozoa; ruminal fermentation.
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