NEW YORK — Federal researchers have developed an unusual strategy for a serious problem among some ranchers: they have taught cows to avoid eating poisonous plants.
Heifers were trained to snub a tasty but toxic plant called the tall larkspur while grazing, and they remembered the lesson the next season.
The tall larkspur may kill more than 2,000 cows a year on high-altitude summer pastures in Colorado, Idaho, Montana, Nevada, Utah and Wyoming, said range scientist Michael Ralphs.
If some remaining obstacles can be overcome, the cow training "is very feasible" for ranchers with a persistent larkspur problem, which can kill up to 10% of a herd, he said.
The approach may also work with other problem plants like locoweed, he said.
Ralphs, of the federal Agricultural Research Service's Poisonous Plant Research Laboratory in Logan, Utah, spoke in a telephone interview before presenting the research at the Third International Symposium on Poisonous Plants, which concluded Saturday in Logan.
Cows relish the flowering plant, which resembles the garden delphinium, said study co-author John D. Olsen.
Ranchers build fences or spray herbicides to fight the problem, both expensive strategies, or they may give up the chance to graze cattle on lush grass and other nutritious plants in larkspur-infested pasture, Ralphs said.
The new work is designed to make cattle associate the taste of tall larkspur with feeling ill. After eating small, safe doses of larkspur, cattle were made to feel nauseous by infusion of a chemical through a tube to their stomachs.
Ralphs said the training made five 1-year-old heifers avoid the plant when turned loose in a small rangeland plot. When they returned the year after training, the aversion persisted.
Yielding to Temptation
But when they were allowed to mingle with untrained cattle that ate larkspur, the trained cows started eating it too.
"Apparently if they observe another animal eating it, they're tempted to try it," Olsen said. 'And if they eat it then without any ill consequence, then the taste aversion is lost, or at least reduced."
To overcome this peer pressure, an additional procedure was tried with five pairs of cattle. One member of each pair was trained, and then the two were offered small doses of larkspur. When the trained animal started eating, it got another dose of the nausea-inducing chemical.
