Methane production by mixed ruminal cultures incubated in dual-flow fermentors.
TL;DR: Dilution rate and forage-to-concentrate ratio altered the partition of substrate by microbes and underestimated methane output at higher dilution rates and with high forage diets.
Abstract: This study evaluated the effects of dilution rate and forage-to-concentrate ratio on gas production by rumen microbes. Continuous cultures were used to monitor methane production at three liquid dilution rates (3.2, 6.3, or 12.5%/h) and three forage-to-concentrate ratios (70:30, 50:50, or 30:70). Filtered ruminal contents were allowed 6 d of adaptation to diets followed by 7 d of data collection. Forage consisted of pelleted alfalfa and the concentrate mix included ground corn, soybean meal, and a mineral and vitamin premix. The experiment was replicated in a split-plot design. Total volatile fatty acid production averaged 58.0 mmol/d and was not affected by treatment. Molar proportion of acetate increased with increasing forage-to-concentrate ratio. Molar proportion of propionate tended to decrease at dilution rate of 12.5%/h and increased with the medium and low forage-to-concentrate ratio. Culture pH tended to be greater at a dilution rate of 12.5%/h. Methane production that was calculated from stoichiometric equations was not affected by treatments. However, methane production based on methane concentration in fermentor headspace resulted in an interaction effect of treatments. Stoichiometric equations underestimated methane output at higher dilution rates and with high forage diets. Total diet fermentability was lowest at dilution rate of 3.2%/h. Increasing dilution rates increased microbial yield; increasing the proportion of concentrate improved microbial efficiency. Dilution rate and forage-to-concentrate ratio altered the partition of substrate by microbes. Methane production based on actual concentrations differed from values estimated using stoichiometry of end-product appearance.
..., 2004) and microbial growth (Eun et al., 2004; Owens and Goetsch, 1986)....
Cites background from "Methane production by mixed ruminal..."
...A large number of old and recent in vitro studies with ruminant inoculum 339 (Isaacson et al. 1975; Shi and Weimer 1992; Meng et al. 1999; Eun et al. 2004; Fondevila and 340 Pérez-Espés 2008) and limited in vivo evidence in domestic cattle (Wiedmeier et al. 1987a; 341 Wiedmeier et al. 1987b;…...
...(Isaacson et al. 1975; Shi and Weimer 1992; Meng et al. 1999; Eun et al. 2004; Fondevila and 340 Pérez-Espés 2008) and limited in vivo evidence in domestic cattle (Wiedmeier et al....
"Methane production by mixed ruminal..." refers background or methods in this paper
...The amount of substrate fermented to VFA, CH4, and CO2 was calculated based on the moles of individual VFA produced, daily methane output, and CO2 released from fermentation and buffer addition (Wolin, 1960; Van Soest, 1994; Blümmel et al., Journal of Dairy Science Vol. 87, No. 1, 2004 1997)....
...Increased lysis of microbial cells as a consequence of substrate exhaustion and uncoupled fermentation may contribute to reduced net growth at longer incubation times (Van Nevel and Demeyer, 1977)....
...Also, total gas yield can vary considerably due to the incorporation of carbons into microbial mass as well as the different metabolic pathways by which carbohydrate fractions can be degraded by rumen microbes (Krishnamoorthy et al., 1991; Beuvink and Spoelstra, 1992; Van Soest, 1994)....
...It is known that the growth yields of ruminal microbes can be relatively high, and that microbial cells have a negative oxidation-reduction state (Van Kessel and Russell, 1996)....
...Stoichiometric equations relating substrate degradation to VFA and gas production have been developed and are commonly used to estimate digestibility of ruminant feeds (Wolin, 1960; Russell and Baldwin, 1979; Menke et al., 1979; Van Soest, 1994)....
"Methane production by mixed ruminal..." refers background in this paper
...The dilution rates tested in the present study were similar to those used by Isaacson et al. (1975) and, therefore, the yield of microbial biomass per mol ATP (YATP) was set to be 7.5, 11.6, and 16.7 mg/mmol ATP for dilution rates of 3.2, 6.3, and 12.5%/h, respectively....
...Hydrogen and CO2 are the major precursors of CH4 formation in the rumen (Hungate, 1967), and most methanogens can utilize these substrates to generate ATP (Thauer et al., 1977)....
...Consequently, microbial biomass from glucose consumption was calculated as: Microbial biomass (g/d) = 0.8 YATP (2 Acetate, mmol/d + 3 Propionate, mmol/d + 3 Butyrate, mmol/d + CH4, mmol/d)/1,000 Energy contents of acetate, propionate, butyrate, valerate, isobutyrate, and isovalerate were used to estimate digestible energy....
...The direct source of CO2 is the fermentation of glucose by various pathways yielding VFA, ATP, and CO2....
...However, changing dilution rates did affect the efficiency of microbial protein synthesis that was reported to be 7.5, 11.6, and 16.7 g of cells/mol of ATP at fractional dilution rates of 2, 6, and 12%/h, respectively (Isaacson et al., 1975)....
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