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The potential of feeding nitrate to reduce enteric methane production in ruminants.  A Report to The Department of Climate Change, Commonwealth Government of Australia, Canberra, ACT, Australia.


Emeritus Professor.
University of New England
Email: rleng@ozemail.com.au

The Australian Government Greenhouse Gas Office commissioned Professor Leng to review the potential to use nitrates in ruminant feeds to limit enteric methane production. A report was submitted to the Governments now Department of Climate Change in October 2008. The major conclusions are:


 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 (NOx) 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

o       Nitrate in the feed is kept within stoichiometric requirements for efficient fermentative digestion

o       Animals are adjusted to nitrate slowly.

o       Previous diet and the production diet are low in readily fermentable (or rumen degradable) protein


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

This report is being up-dated and corrected on a continuous basis and has been modified slightly compared to the report posted on the Department of Climate Change website that can be accessed at http://www.climatechange.gov.au/

For the full report click here

For a Power-point  presentation click here.

Older publications and presentations.

Follow the links to the left or click here  to read about Prof R.A Leng's latest publication "Drought and Dry Season Feeding Strategies for Cattle, Sheep and Goats".

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Last modified: 10/10/05