Hundreds of sheep in the central west of New South Wales, Australia, have died after eating a poisonous plant and bashing their heads open "like heroin addicts". Plague proportions of darling pea have dealt another blow to farmers who suffered the impacts of the bushfire in Coonabarabran last January. The endangered native pea, which usually exists in the area in small quantities, has spread wildly following the bushfire, which burnt 54,000 hectares of the Warrumbungle National Park and adjoining farms.
Stephen and Louise Knight have lost 800 sheep to the noxious plant so far on their steep, rocky property, Tannabah.
"We counted 800 missing wethers at shearing time," Mrs Knight said. "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." Darling pea, from the Swainsona species, is a stout-stemmed, erect plant with purple pea-shaped flowers and long woolly pods.
The Swainsona species contain a poison that is toxic to livestock. When grazed on for extended periods of time, the plant's toxins build in the animals' systems and affect their central nervous systems by attacking an enzyme involved in metabolism. North West Local Land Services regional veterinarian Bob McKinnon said the stock became addicted to the plant and displayed erratic 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 and they become recumbent and die that way," he said. Other symptoms the affected animals display include staring eyes, head pressing, muscle tremors, walking with a paddling gait, high stepping, and dragging hind legs.
Mrs Knight said the symptoms were evident. "They just go to a post and bang their head on it till they crack their heads open; it's like dealing with a thousand heroin addicts," she said. With stock in this condition, paddocks that once took the Knights six hours to muster now take them days. Unfortunately, Mr McKinnon said there was no easy cure for the affected animals. "The cure is to get the animals off it," he said. "Once you take them off it they are no longer exposed to the substance that is blocking the enzyme and the cells can then repair themselves. But if they've been on it too long the damage has been done and it doesn't repair to where it should be."