SYDNEY – When Australian farmer Tony Knight first saw a purple-flowering plant growing across the fire-scarred terrain where his sheep grazed, his first thought was that it looked like “good stock feed.”
But the “pleasant-looking plant” was far from the nutritious food his livestock needed after their paddocks were razed bare by fires that swept through New South Wales state in the northwest last year. The weed, known as the Darling pea, contains a toxin that affects the sheep’s nervous systems, and it has been blamed for killing hundreds of animals by triggering mental and physical deterioration.
“To start with, they will do quite well when they first get onto it, and their condition will pick up,” Knight said from his farm near the town of Coonabarabran. “But once it gets them addicted, it’s just a drug — it goes from becoming their best friend to their worst enemy.”
Knight has lost almost 100 merino sheep out of an 800-strong flock to the noxious pea in recent months. His sister-in-law, Louise, who lives on the farm next door, said 800 of her 14,000 sheep died after eating the plant.
A confluence of events enabled the outbreak, with the weed growing in an area where bush fires wiped out competition by other plants. The destruction of fences during the fires meant the animals roamed the mountainous terrain, chewing the weed wherever they went.
Knight, whose family has lived on the land beside Warrumbungle National Park for generations, said the affected sheep were easy to spot. “You will see them in a paddock — usually they are on their own. They do a lot of star gazing. They do a lot of trotting around with their heads in the air. The dogs get very confused because they don’t behave like they should.” He said some sheep “didn’t know which planet they were on. They were all spaced out.”
Veterinarian Greg McCann said the toxin attacks an enzyme involved in metabolism in the brains of affected animals.
“They lose the ability to judge where their feet are. They become wonky, fall over, appear to be blind, walking into things,” McCann told the rural newspaper The Land. “They can assume funny postures, like head bent down or head bent back, but the one thing that was seen in the cases associated in the Coonabarabran area were twitching.”
Knight said so far there appeared to be one solution to weed out most of the pea: by getting the sheep to eat them. “It’s ironic, but it seems that the best way to control it is with livestock,” he said. “It’s a perennial plant, and if something eats it, it will shoot again. As it shoots, if there is something there to eat those shoots, it won’t take long before they kill a plant.”