By Martin Cassidy
BBC NI consumer affairs correspondent
Every cow belch is counted and sampled by a special valve
The cows make a greedy rasping sound as they graze but even with their heads down it is clear the cattle at the Agricultural Research Institute at Hillsborough are wearing an unusual contraption around their head and neck.
Gently one raises its head, swishes its tail and burps, sending a stream of colourless and odourless greenhouse gas into the atmosphere.
But every belch is counted and sampled thanks to a special valve strapped on the muzzle.
The special headgear also holds in place a storage chamber which allows the scientific team led by Dr Conrad Ferris to measure the volume of methane gas produced by the institute's herd of milkers.
And the results are surprising and for environmentalists more than a little alarming.
It turns out that in a single day a cow can burp and belch a staggering 400 litres of methane into the atmosphere.
A discreet inquiry reveals that most of the gas comes out of the cow's mouth - well over 90% apparently.
Should we be worried about all this gas?
Well it seems we should, not least because methane has a greater greenhouse effect than CO2.
Every burp from Northern Ireland's 1.6m cattle delivers a planet-warming dose of gas into the atmosphere - gas which is particularly good at trapping heat from the sun and so adding to the problem of global warming.
"It all happens in the rumen where the cow digests much of of the fibre it consumes," says Dr Ferris.
Already the research team has found that changes to the cow's diet can reduce the amount of greenhouse gas it produces.
And that may prove to be important for the local economy.
With a replacement for the Kyoto agreement being negotiated it may mean Northern Ireland can keep its cattle herd intact while still meeting reductions in methane emissions.
Much remains to be discovered about cows and their gaseous digestive tracts but with pressure to reduce global warming, the cows at the Argi Food and Biosciences Institute are helping local farming prepare for the day when greenhouse gas reductions may become mandatory.