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Toxic plants cost ranchers $300M a year; management key to prevention

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Identifying toxic plants on rangeland is the first step, researchers say.

TWIN FALLS, Idaho — Livestock deaths and other expenses related to toxic plants cost Western ranchers more than $300 million annually, researchers say, and the best way to reduce the impact is through better management.

Those direct losses result from death, abortion, birth defects and reduced animal productivity. But there are also indirect losses, such as costs related to veterinary services, fencing and altered grazing plans, Jim Pfister, USDA-ARS research rangeland management specialist, told livestock producers at the University of Idaho Range Livestock Symposium last week.

Pfister is part of a team at USDA’s Poisonous Plant Research Laboratory in Logan, Utah, that takes an interdisciplinary approach to solving poisonous plant issues.

“It’s important to remember that the dose makes the poison. All substances are a poison,” he said.

Some plants are only toxic under certain conditions, such as certain stages in the plant’s life cycle or how they are ingested, he said.

Many toxic plants flourish on rangelands across the Intermountain West. Some of the most problematic include larkspur, locoweed and lupine.

“Larkspur probably kills more cattle on Western ranges than any other plant,” he said.

Losses are typically 3 to 5 percent annually but can be as high as 10 to 20 percent in an individual herd. Cattle generally like larkspur, and at some point in the season they’ve probably all been eating it, he said.

Toxicity is problematic because it varies greatly from plant to plant and year to year. Toxicity decreases as the season progresses and drops significantly after the first frost. Clinical signs of toxicity in livestock include staggering gate, muscle tremors and lying down.

Whether it causes cattle to drop or die depends on how much they eat, how fast they eat it, the amount of toxic alkaloid in the plant, how many consecutive days they’ve eaten it, how much they move around after ingesting it — exercise exacerbates the effects — and individual susceptibility.

The toxin in the plant can paralyze the diaphragm and cattle can die from bloat or respiratory failure, he said.

Adequate moisture this year indicates a good year for larkspur, which could reduce grazing options to the early and late seasons. Cattle typically eat the plant after it flowers — a window of high risk when it is palatable and toxin levels are moderate — so ranchers could graze the area before that window and later, when the plant is in the late pod stage, he said.

The plant is not toxic to sheep, so they could also graze sheep ahead of cattle to reduce how much is available to cattle.

Herbicide control can be used if it’s allowed, and drug therapy is available but cattle can relapse and need more than one treatment.

Grazing management plays an important role in reducing livestock losses, but researchers are doing genetic testing in cattle for resistance and susceptibility to larkspur.

“There is a tremendous amount of variability within and between breeds,” he said.

The research is exciting and could lead to genetic selection for resistance, he said.

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