KEY POINTS:
Cows have emerged as the world's top destroyer of the environment.
A United Nations report has identified the world's rapidly growing herds of cattle as the greatest threat to the climate, forests and wildlife.
And they are blamed for a host of other environmental crimes, from acid rain
to the introduction of alien species, from producing deserts to creating dead zones in the oceans, from poisoning rivers and drinking water to destroying coral reefs.
The report by the Food and Agricultural Organisation, entitled Livestock's Long Shadow, also surveys the damage done by sheep, chickens, pigs and goats.
But in almost every case, the world's 1.5 billion cattle are most to blame. Livestock are responsible for 18 per cent of the greenhouse gases that cause global warming, more than cars, planes and all other forms of transport put together.
Producing fertiliser to grow feed, to farm meat and to transport it - and clearing vegetation for grazing - produces 9 per cent of all emissions of carbon dioxide, the most common greenhouse gas.
And their wind and manure emit more than one third of emissions of another, methane, which warms the world 20 times faster than carbon dioxide.
Livestock also produces more than 100 other polluting gases, including more than two-thirds of ammonia emissions, one of the main causes of acid rain.
Ranching, the report adds, is "the major driver of deforestation" worldwide, and overgrazing is turning a fifth of all pastures and ranges into desert.
Wastes from feedlots and fertilisers used to grow feed overnourish water, causing weeds to choke all other life. And the pesticides, antibiotics and hormones used to treat them get into drinking water.
The report concludes that, unless drastic changes are made, the damage done by livestock will more than double by 2050, as demand for meat increases.
There are about 10 million cows in New Zealand and farmers here question the report's findings.
"I suspect it is written by a vegan," Federated Farmers president Charlie Pedersen said. "We are not talking about cattle, we are talking about food.
"If you take that food off the market, you have to replace it with something else. You still have to eat. It's a very narrow way of looking at things."
Graham Fraser, chairman of Dairy 21 - a group reviewing dairy farming productivity within its environmental constraints - said he found the report's finding on cows "extraordinary".
"The cow has been a tremendous servant to human kind for so long, converting grass into something we can eat."
- INDEPENDENT, additional reporting Jarrod Booker