Thousands of sheep in Australia are believed to have died after eating a poisonous plant that makes them “bash their heads on posts and rocks until they crack open”.

The usually-rare toxic plant, misleadingly named the “Darling pea”, has spread rapidly in the aftermath of bushfires in New South Wales – which themselves caused devastation for sheep farmers in the area.

Now vets have said that many of the animals which survived the fires face a new and highly addictive threat.

North West Local Land Services regional veterinarian Bob McKinnon told the Sydney Morning Herald that once sheep started eating the plant they exhibit behaviour “similar to that of a drunk”.

“They lose weight to start with and then get staggery, the progression gets worse, they get unco-ordinated and depressed, they don't know where their feet are.”

He said that “staring eyes”, “head pressing” and “muscle tremors” were other symptoms, until eventually the animals “just go to a post and bang their head on it till they crack their heads open”.

The task of bringing in herds that would normally take six hours instead takes “days”, Mr McKinnon said. “It’s like dealing with a thousand heroin addicts.”

Just one farming family in Coonabarabran said they had lost 800 sheep to the deadly plant. Stephen and Louise Knight said the animals were missing when they counted up the stock at shearing time.

“It was just devastating they weren't there when we went to get them.

“The fire was a distressing thing to have happen, we lost so many stock, fences, pasture - and then for it to come back with a terrible noxious plant like this, it's awful and very distressing.”

The plant, from the Swainsona family of desert peas native to Australia, has toxins which build up when sheep graze on it for extended periods. It attacks an enzyme involved in metabolism, ultimately crippling the animal’s central nervous system.

There is no cure, Mr McKinnon said, other than to “get the animals off it in time”. “But if they've been on it too long the damage has been done and it doesn't repair to where it should be,” he said.

Independent News Service