Effects of select nitrocompounds on in vitro ruminal fermentation during conditions of limiting or excess added reductant

Ruminal methane (CH4) production results in the loss of up to 12% of gross energy intake and contributes nearly 20% of the United States' annual emission of this greenhouse gas. We report the effects of select nitrocompounds on ruminal fermentation after 22 h in vitro incubation (39 degrees C) with or without additions of hydrogen (H-2), formate or both. In incubations ontaining no added reductant, CH4 production was inhibited 41% by 2-nitro-1-propanol (2NPOH) and >97% by 3-nitro-1-propionic acid (3NPA), nitroethane (NE) and 2-nitroethanol (2NEOH) compared to non-treated controls and H-2 did not accumulate. With formate as the sole added reductant, nitro-treatment reduced CH4 production by >99% and caused 42% to complete inhibition of formate catabolism compared to controls, and the accumulation of H-2 increased slightly. Nitro-treatment decreased CH4 production 57-98% from that of controls when supplied H-2 or formate plus H-2. Formate catabolism was decreased 42-84% from that in controls by all nitro-treatments except 3NPA with both formate and H-2. Greater than 97% of the added H-2 was catabolized within controls; >84% was catabolized in nitro-treated incubations. Acetate, propionate and butyrate accumulations were unaffected by nitro-treatment irregardless of reductant: however, effects on ammonia and branched chain fatty acid accumulations varied. These results suggest that nitro-treatment inhibited formate dehydrogenase/formate hydrogen lyase and hydrogenase activity. Published by Elsevier Ltd.