The acute effect of addition of nitrate on in vitro and in vivo methane emission in dairy cows

The effects of a 24-h administration of a ration high in nitrate (20 g/kg DM) on DM intake and enteric gas production in lactating dairy cows as well as the effect of different doses of nitrate on in vitro fermentation were studied. Nitrate reduced in vivo methane (CH4) production by 31%, and CH4 production increased again when nitrate supplementation was stopped. A similar effect was found when relating CH4 to carbon dioxide, and to DM intake. Addition of nitrate was followed by increased hydrogen production, which decreased again when nitrate was stopped. Nitrate addition did not affect in vitro rumen fermentation in terms of DM degradability, pH, ammonia nitrogen, microbial protein and volatile fatty acid production, but it decreased gas production with longer initial delay time before onset of gas production and lower gas production rate. Nitrate added at 7-20 g/kg ration DM significantly decreased net initial (0-12 h) CH4 production by 10-16%, although no further depression was observed afterwards.