Methane (CH4) is a greenhouse gas, as well as an energy loss in ruminant animals. Much research has been done aimed to reduce CH4 emission from cattle industry. Nitrocompounds such as nitroethane (NE), 2-nitroethanol (2NEOH), and 3-nitropropionic acid (3NPA), have been shown to possess the ability to inhibit methane production on in vitro conditions. However, the potential of ethyl-2-nitropropionate (E2NPA) and ethyl nitroacetate (ENA) to reduce methane production have never been evaluated. We evaluated the ability of ENA, E2NPA, 2NEOH, and NE to reduce total gas, CH4 production and microbial diversity changes in a consecutive batch culture. Mixed populations of ruminal bacteria were incubated in tubes 18 × 150 mm containing a basal medium with 0.2 g of ground alfalfa and a H₂/CO₂ (1:1) gas phase. Tubes were supplemented with water (control) or the corresponding nitrocompound to reach a 12 mM concentration and incubated at 39°C. Total gas production was determined after 24 h. Microbial diversity was determined by DGGE. Gas composition was determined by gas chromatography. Data were analyzed using PROC GLM of SAS by a complete randomized design considering each nitrocompound as sole effect. According to our results, the use of nitrocompounds as supplement had no significant effect on total gas production, except for nitroethane (P ≤ 0.000; Table 1). In the other way, methane production was decreased (P ≤ 0.0001) by all nitrocompounds compared with the controls. In addition, each nitrocompound does not showed difference on its capacity of reducing methane emissions (P ≤ 0.05). The DGGE indicates that all nitrocompounds change the microbial diversity. Results of the study also reveal that the capacity of ENA and E2NPA to decrease methane production is very similar to the 2NPOH and NE. There is some evidence that these nitrocompounds could be supplemented to reduce methanogenesis. Table 1.

Treatment (nitrocompound)	Total gas volume production (mL)	Reduction (%)	Methane (µM/mL)	Reduction (%)
Control	19.00	—	43.77	—
Ethyl nitroacetate	18.10	4.73	1.41	96.80
2-Nitropropionate	18.79	1.10	1.06	97.70
2- Nitroethanol	18.36	3.36	1.17	97.33
Nitroethane	15.40	18.94	1.83	95.86