Scientists at Gramina, a joint biotech venture by Australia’s Molecular Plant Breeding Cooperative Research Centre and New Zealand rural services group PGG Wrightson Genomics, are developing a grass that will not only cut the amount of methane cows burp up when chewing the cud but will also grow in hotter climes, according to the latest issue of Chemistry & Industry.

This means that farmers should be able to maintain dairy herds’ productivity and profitability in the face of a changing climate, while cutting down their gaseous burps and reducing their contribution to global warming.

Combating greenhouse gas emissions produced by the agricultural industry is a priority. The UK’s DEFRA has just announced a roadmap aimed at helping the dairy industry reduce its potential impact on the environment in line with Britain’s target to cut its greenhouse emissions by 20% by 2010. By 2015 the roadmap plans to have 20-30% of milk producers trialling new technology to cut greenhouse gas emissions.

The Inter-governmental Panel on Climate Change (IPCC) calculates that methane makes up 14.3% of humanity’s contribution to global warming and data from the National Oceanographic and Atmospheric Administration (NOAA) in the US shows that atmospheric methane levels may be rising again after a 10 year period of stability. A single dairy cow can produce between 550-700L of methane a day and it has been estimated that methane from cattle in the UK could account for as much as 3% of the country’s total greenhouse gas emissions.

Cows’ production of methane is down to the microflora in their gut that helps them to digest their food. As these microbes break down the grass’ cellulose, methane is produced as a by-product, the majority of which is burped up.

David Beever, international nutrition director of Richard Keenan UK, said: ‘You don’t actually hear the cows burp, but they are permanently releasing methane.’

Gramina will use sense suppression technology to prevent the expression of the enzyme O-methyl transferase. Suppressing this enzyme leads to an increase in the digestibility of the grass without compromising its structural properties and therefore less burps and less methane.

Gramina has already tested this modification in temperate grasses in the lab and glasshouses and is now planning field trials.

However, some scientists suggest that a cow’s absolute methane emissions might go up.

Alistair Macrae, a lecturer in farm animal health and production at the University of Edinburgh, UK, says a diet too rich in highly digestible carbs can actually increase the amount of methane a cow belches out. This is because gut microflora convert more of these sugars into propionic acid, which creates a more acidic environment resulting in more methane.

Ian Givens, a professor of animal science, at the University of Reading, UK, says that more digestible forage could push up a cow’s absolute methane emissions but productivity gains would mean less methane per unit of milk.

Beever agrees and says, ‘It could increase methane emissions but it could also increase milk yields, effectively cutting the amount of methane produce per litre of milk.’