|Carstens, G - TX A&M UNIVERSITY|
Submitted to: Conference on Gastrointestinal Function
Publication Type: Abstract Only
Publication Acceptance Date: January 24, 2005
Publication Date: April 11, 2005
Citation: Anderson, R.C., Carstens, G.E., Callaway, T.R., Schultz, C.L., Edrington, T.S., Nisbet, D.J. 2005. Effect of intraruminal nitroethane administration on methane-producing activity and volatile fatty acid production in vivo [abstract]. Conference on Gastrointestinal Function. p. 23. Technical Abstract: Strategies are sought to reduce economic and environmental costs of ruminal methane production, an inefficient digestive process resulting in the loss of 2 to 15% of gross energy intake. The effect of nitroethane, a recently discovered inhibitor of methanogenesis, on methane-producing activity and volatile fatty acid production was evaluated in two ruminally cannulated Holstein cows maintained on rye grass pasture and provided ad libitum access to mineral supplementation. Each cow was administered 120 mg nitroethane/kg body weight per day for 8 d. Nitroethane was administered intraruminally as the sodium salt in two equal sized portions (08:00 and 16:00). Methane-producing activity, an indirect measure of numbers of methanogenic bacteria, was determined at the indicated intervals via in vitro incubation (39 deg C for 3 h) of rumen fluid or feces (5 or 2 g, respectively) in anaerobic buffer (5 or 10 ml, respectively) containing 60 mM sodium formate, 0.2 g finely ground alfalfa and a H2:CO2 (50:50 mix) atmosphere. Ruminal methane-producing activity was reduced 2.9, 2.3, 2.0, 4.7, 5.8, 7.6 6.1, 2.7 and 1.4-fold from pre-treatment measurements (0.44 ± 0.01 micromol CH4/g rumen fluid per h) at 2, 8, 16, 24, 48, 72, 96, 168 and 192 h of treatment, respectively. Thus, nitroethane markedly reduced ruminal methane producing activity within the first four days of treatment but was diminished by day 8 of treatment suggesting a ruminal adaptation to nitroethane. At least one ruminal microbe (Denitrobacterium detoxificans) is known to metabolize nitroethane, coupling its reduction to the oxidation of hydrogen or formate. In contrast, fecal methane-producing activity differed little from pre-treatment measurements (0.17 ± 0.10 micromol CH4/g feces per h) at 8 and 16 h of treatment but was increased 9.9, 5.6 and 7.7-fold from pretreatment measurements by 48, 72 and 96 h of treatment, respectively. By 168 and 192 h of treatment, however, fecal methane producing activity was only 0.5 and 1.1-fold higher than pretreatment measurements. These data suggest an initial but temporary displacement of methanogenic bacteria from the rumen to the lower gut. Ruminal volatile fatty acid concentrations fluctuated during the course of the study but molar proportions of acetate to propionate differed little throughout the study. Thus, electrons produced during fermentation were not disposed of via production of more reduced fermentation acids but possibly were consumed by other reductive processes such as the reduction of nitroethane to aminoethane.