Effects of oral nitroethane administration on enteric methane emissions and ruminal fermentation in cattle

Methane is a potent greenhouse gas and its release to the atmosphere is widely believed to contribute to global warming. Ruminal enteric CH4 production represents a loss of 2-15% of the animal's gross energy (GE) intake and contributes nearly 20% of US CH4 emissions. Studies have evaluated the CH4 inhibiting potential of select short chain nitrocompounds, such as nitroethane, but results demonstrating their effects on ruminant exhaled CH4 emissions are lacking. Our study determined effects of oral nitroethane administration on CH4 emissions, accumulations of volatile fatty acids (VFA) and on ruminal CH4 producing activity in steers fed a forage based diet containing 8.8 MJ/kg of metabolizable energy on a dry matter (DM) basis. Effects of nitroethane administration on ruminal nitroethane reducing activity were also determined. Holstein steers (n = 24) of 317 +/- 6.5 kg body weight (BW) were assigned to 4 treatments that included: 0, 30, 60 and 120 mg nitroethane/kg BW/d. Treatments were administered via oral gavage twice daily at 08:00 and 16:00 h for 8 d. DM intake decreased quadratically as level of nitroethane increased with steers administered 60 and 120 mg nitroethane/kg BW consuming 14 and 7% lower DM, respectively, than steers administered 0 or 30 mg nitroethane/kg BW. Methane emissions as a proportion of GE intake and ruminal CH4 producing activity both decreased linearly (P<0.001) as level of nitroethane increased. Compared to control steers, daily administration of nitroethane at 60 and 120 mg/kg BW reduced CH4 emissions as a proportion of GE intake 9-22% and ruminal CH4 producing activity 24-26%. Ruminal VFA accumulations were unaffected by nitroethane treatment. Results demonstrate that short term oral administration of nitroethane may be an effective anti-methanogenic compound in steers fed high forage diets. Further research is warranted to determine if strategies using nitroethane lower enteric CH4 emissions in ruminants long term. Ultimately, nitrocompounds which can be reduced by rumen microbes to yield compounds with nutritional value for the host, such as amino acids, would be preferred. This paper is part of the special issue entitled: Greenhouse Gases in Animal Agriculture - Finding a Balance between Food and Emissions, Guest Edited by T.A. McAllister, Section Guest Editors: K.A. Beauchemin, X. Hao, S. McGinn and Editor for Animal Feed Science and Technology, P.H. Robinson. Published by Elsevier B.V.