Effects of nitroethane and monensin on ruminal fluid fermentation characteristics and nitrocompound-metabolizing bacterial populations

Authors: GUTIERREZ-BANUELOS, HECTOR - TX A&M UNIVERSITY; Anderson, Robin; CARSTENS, GORDON - TX A&M UNIVERSITY; TEDESCHI, LUIS - TX A&M UNIVERISTY; PINCHAK, WILLIAM - TX AG EXPERIMENT STATION; CABERA-DIAZ, ELISA - TX A&M UNIVERSITY; Krueger, Nathan; Callaway, Todd; Nisbet, David

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/17/2008
Publication Date: 6/25/2008
Citation: Gutierrez-Banuelos, H., Anderson, R.C., Carstens, G.E., Tedeschi, L.O., Pinchak, W.E., Cabera-Diaz, E., Krueger, N.A., Callaway, T.R., Nisbet, D.J. 2008. Effects of nitroethane and monensin on ruminal fluid fermentation characteristics and nitrocompound-metabolizing bacterial populations. Journal of Agricultural and Food Chemistry. 56:4650-4658.

Interpretive Summary: Cows and sheep contain beneficial bacteria in the front part of their stomach that can degrade the strong chemical bonds that make grasses hard to digest. Unfortunately, this digestion is inefficient in that methane is produced as an end-product that is not able to be used by the cattle or sheep. This digestive inefficiency can result in as much as 12% of the dietary energy being lost. Methane is also a greenhouse gas that may contribute to climate change. Consequently, animal nutritionists and microbiologists have long sought to develop ways to reduce the amount of methane produced in the forward part of the cow and sheep stomach. We report results from an experiment testing the effectiveness of two chemicals that reduce methane when fed to cows. We found that a chemical called nitroethane significantly reduced methane production by approximately 90% and was better than a commonly used antibiotic chemical called monensin. We also found that the chemical nitroethane did not negatively affect beneficial end-products of the microbial digestion process as is sometimes observed with the antibiotic monensin. Our results suggested that this was because a special nitroethane-using bacterium able to outcompete methane-producing bacteria was increased in number by the nitroethane treatment but not by the monensin treatment. While naturally present in the cow and sheep gut, this bacterium is usually very low in number. Thus, the nitroethane treatment appeared to an effective strategy because it replaced methane-producing bacteria with another naturally present beneficial bacterium without inhibiting other important bacteria needed for digestion while at the same time maintaining a healthy gut environment. These results will help scientists and farmers develop ways to cut production costs and help the environment by reducing animal methane production without using antibiotics. Ultimately, these results may help farmers and ranchers produce safe and wholesome beef and lamb products at less cost for the American consumer.

Technical Abstract: The objectives of this study were to examine the effects of nitroethane (NE) and monensin (M) on ruminal fermentation, NE-degradation and nitro-degrading bacterial populations during in vitro consecutive batch culture (CBC). Treatments tested included control (C), 4.5 mM NE (1NE), 9 mM NE (2NE), 5 mM M (M), and 9 mM NE plus 5 mM M (2NEM). Cultures were incubated at 39 deg C under H2:CO2 (1:1) and transferred at 24 h intervals over 16 incubation series. Methane (CH4), carbon dioxide (CO2) and hydrogen (H2) productions (umol/mL) were measured in the head space after series 1, 2, 3, 6, 10, 13 and 16; NE-degradation, volatile fatty acids (VFA), ammonia (µmol/mL) and lactate (mg/dL) were measured after series 1, 2, 3, 6 and 10, and most probable number (MPN) determination of nitro-degrading bacterial populations after the 6th series. After the 16th series treatment, a cross over experiment was conducted to measure response of the previously treated populations during culture in absence of respective supplements. Methane production was affected (P < 0.01) by treatment, with accumulations averaging 8.48, 0.88, 0.81, 1.88 and 0.74 (± 0.37 SEM) for C, 1NE, 2NE, M and 2NEM, respectively. Carbon dioxide decreased with 2NEM, but no differences were observed on 1NE, 2NE, and M in comparison with C (67.78, 89.00, 83.37, 74.93 and 99.94 ± 5.30 respectively). No effect treatment was observed on H2 accumulation (P > 0.05). Acetate and propionate were not affected (P > 0.05) by treatment. Butyrate accumulation was lower (P < 0.05) with the addition of M and 2NEM and higher (P < 0.05) with 1NE and 2NE in comparison with the C (1.73, 1.89, 5.65, 6.10, and 4.81 ± 0.73, respectively). NE-degradation (umol/mL) was higher (P < 0.01) with 2NEM in comparison with 1NE and 2NE (1.26, 0.41 and 0.95 ± 0.06, respectively). The MPN of nitro-degrading bacterial populations were increased (P < 0.01) in 1NE and 2NE supplemented incubations (6.9 and 5.9 log10 cells/mL, respectively) compared to C, M and 2NEM supplemented incubations (< 2.5 log10 ± 0.8 cells/mL). The cross over experiment showed that methane-producing activity was no longer present in the mixed populations that had been incubated the previous 16 transfers with NE, as evidence by a lack of CH4 accumulation on the 17th transfer into medium not containing the CH4-inhibitor NE. In contrast, methanogens were present in the populations that had been cultured 16 times with monensin, as evidenced by considerable CH4 accumulation upon removal of selective pressure of monensin. These results confirm the CH4-inhibiting activity of NE and monensin and suggest that ruminal adaptation of bacteria to NE is likely due to an enrichment of nitro-degrading bacteria. These results also provide evidence that monensin negatively affects nitro-degrading bacterial populations.