Methane accumulation in the atmosphere only requires a slowing of emissions by 15-20 per cent for world atmospheric concentrations to stabilize and possibly decrease. One way to reduce the massive contribution to global warming from the world’s 3.6 billion ruminant livestock is to feed them on nitrates.

Methane, produced and released into the atmosphere from many biological systems is a greenhouse gas which has about 21 times more capacity to retain heat than carbon dioxide, the major green house gas. Globally ruminants produce some 80 million tonnes of methane annually, or 28 per cent of anthropogenic (man made) methane emissions. Clearly the adoptions of management practices for ruminants which achieve major reductions in methane production by ruminants are issues of high priority.

In ruminants, the production of methane is an inevitable consequence of their digestion processes which occurs in an enlarged forestomach (the rumen) where feed is held for some time and digested by microbes. The rumen microbes that digest the feed for the animal have to dispose of hydrogen produced in fermentation, because its accumulation would inhibit the continuous digestion of feed. This is accomplished by specialised micro-organisms that reduce carbon dioxide to methane.

The research evidence leaves little doubt that nitrate, when included at sufficient concentrations in a diet so as to maintain optimum feed intake, can largely prevent enteric methane production from ruminants.

A barrier to its use in practice is nitrite poisoning.  However, nitrite production only occurs when relatively large quantities of nitrate are suddenly introduced into an animal’s diet or when ruminants are fed high protein forages; in the latter the use of any crude protein supplement is irrational. Research has focused attention on the toxicology of nitrite poisoning and this has stifled research on its nutritional attributes as a useful supplement to ruminant animals that will lower methane production.

Urea has been a major source of crude protein fed to ruminants and animals must be adapted to it  over a number of days to avoid toxicity. For many years urea was also placed in a category of potentially toxic substances but which is now included in the diet of millions of ruminants world wide. In fact Dr Artturi Virtanen received a Nobel Prize for demonstrating that dairy cows can produce moderate amounts of milk when fed high carbohydrate diets with urea as the sole source of crude protein. It appears that this may be possible now by feeding nitrate, without production of methane. In short, the scientific literature indicates that nitrite poisoning is not a threat to well managed livestock if they are first conditioned to and then continuously maintained on this  crude protein source.

The world population of ruminant livestock approximates 1800 million cattle equivalents (8 goats or sheep equalling I cattle equivalent), over 50 per cent of these are in developing countries where they are largely fed on poor quality feeds. The vast majority of ruminants in developed countries are also fed under circumstances where they require supplementation with crude protein to optimise productivity either in dry seasons or when fed cereal grains. Feeding urea to ruminants on diets deficient in crude protein increases productivity and reduces the methane produced per unit of product. The replacement of urea with salts of nitrate will further reduce methane production significantly, possibly on some diets by as much as 100 per cent. In short, it turns more of the feed into meat or milk, with less wasted energy in the form of methane – and so, less greenhouse gas produced.

It is difficult to assess the contribution of a successful methane mitigation program of feeding nitrates instead of urea to ruminants, but if implemented worldwide on low producing animals that are constrained by the crude protein in their diets, then it could be that methane production could be reduced to the extent that atmospheric levels could progressively decline provided other sources do not come on line (for example methane hydrates in melting ice caps). 

FAO forecasts that meat production will need to be doubled by 2030 to meet world population increase. The competition for grains (or crop land) for food for humans, feed for animals or feedstock for biofuel production indicates that grain will be too expensive  and that much of this extra meat must be generated from biomass resources which are presently underutilized. These, largely cellulose (fibrous) residues, can only be used by herbivores - in particular the ruminant - by virtue of their fermentative digestive system if they are also fed with supplements of crude protein such as urea.

Recent developments in the industrial processing of crop residues to improve their feed value have pioneered the way for the future expansion of ruminant production without impinging on land use for human food production. These systems will need to be expanded to fill the coming gap in meat production. However, the additional enteric methane production will be a major drawback. If urea can be replaced with nitrate as the main crude protein source this will reduce enteric methane production significantly, will improve the yields of meat, milk and fiber we obtain and will increase the acceptability of these novel production systems.
 
In short, the use of nitrate in non-conventional feeds which are low in crude protein appears to be entirely feasible. Major ruminant meat and milk producing industries based on treated cereal crop wastes, sugar cane, molasses and cassava have enormous potential to provide quality protein for future human consumption – with far less penalty to the global climate. The potential significance of methane-less meat, milk and wool production needs to be explored.

See www.penambulbooks.com for the full report submitted to The Department of Climate Change.

Dr Ron A Leng AO, PhD, DRurSc is Emeritus Professor at the University of New England.