Nitrate reduction to ammonia can replace the reduction of carbon dioxide to methane as a major sink for disposal of hydrogen in the rumen when included in suitable amounts in ruminant diets.
 

Nitrate as a sole fermentable N source in a diet could totally inhibit enteric methane production by ruminants.
 

The barrier to the use of nitrate in the diet of ruminants to reduce enteric methane production is the potential for the accumulation of nitrite in the rumen that is anti-nutritional and can cause reduced productivity and even death when absorbed.
 

Nitrite accumulation and nitrate poisoning are not encountered when animals are adjusted to nitrate in the diet over a period of about a week.
 

Nitrate can be potentially most efficiently used to lower methane production in diets that require some form of nitrogen supplementation to optimise feed intake.
 

Nitrate could be applied to the large numbers of animals that are fed poor quality diets which  produce most of the enteric  methane in the world.
 

The use of nitrate in high protein feeds is unlikely to be practical. It appears that excess protein predisposes the generation of nitrite from nitrate in the rumen. It would also be illogical to add extra nitrogen into such diets that would inevitably increase the excretion of N by the animal, potentially leading to release of nitrogen oxides/methane from the excreta. Nitrogen oxides (NO_x) being considerably more potent green house gas than methane.
 

The reason for nitrite accumulation in the rumen needs to be explained. Drawing on studies from natural anaerobic ecosystems amended with nitrate it is hypothesized that nitrite production in the rumen when nitrate is fed, results from a single group of organisms. These reduce nitrate to ammonia using sulphide to reduce the intermediate nitrite (they are nitrate reducing sulphide oxidising bacteria termed NR-SOB). At high nitrate concentrations in a diet, nitrate reducing bacteria (NRB) that abound in the rumen effectively inhibit sulphur reducing bacteria (SRB) and lower hydrogen sulphide concentrations in the rumen. Low availability of hydrogen sulphide inhibits or slows NR-SOB reduction of nitrite to ammonia resulting in nitrite accumulation in the rumen. It is proposed that the population density of NR-SOB is governed by previous diet depending on nitrate and protein levels in the feed.
 

Nitrate can be safely used to lower methane production in ruminants provide the following conditions are met

The conditions and precautions for feeding nitrate are precisely the same for the safe use of urea in ruminant feeds.