Australian Sheep Addicted to Toxic Plants Committing Mass Suicide
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New South Wales farmers Stephen and Louise Knight have watched as 800 of their sheep have killed themselves after grazing on the darling pea, a purple upright plant that's toxic to livestock and over time causes addiction, lack of coordination, and depression.
Once their addiction has become unbearable, the sheep will bash their heads open against a fencing post. "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," said Louise Knight. "It was just devastating.”
The darling pea, also known as Swainsona greyana, is a rare native plant to Australia that has typically been confined to relatively small areas of the country. But rampant brush fires in 2013 have wiped out the plant’s competition and allowed it to spread rapidly across New South Wales.
The plant contains the alkaloid swainonine which causes alpha-mannosidosis, a build-up of toxins that results in displays of erratic behavior, including staring eyes, head pressing, muscle tremors, and dragging their hind legs.
"They lose weight to start with and then get staggery,” said regional veterinarian Bob McKinnon from the North West Local Land Services. “The progression gets worse, they get uncoordinated and depressed, they don't know where their feet are and they become recumbent and die that way."
Other farmers besides the Knights have experienced similar tragedies with their own livestock, with estimates concluding that thousands of the region’s sheep have been affected. According to McKinnon, there is very little to do other than “get the animals off it in time”.
"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,” he said. “But if they've been on it too long the damage has been done and it doesn't repair to where it should be.”