Cooler days turn grazing toxic

Cattlemen on lookout for johnsongrass, other hazards

John Pennington, executive director of the Beaver Watershed Alliance, works with a group of volunteers in July to cut the seed heads off of johnsongrass. The grass can become toxic to livestock.
John Pennington, executive director of the Beaver Watershed Alliance, works with a group of volunteers in July to cut the seed heads off of johnsongrass. The grass can become toxic to livestock.

As cooler temperatures descend on the state, some summer plants can become toxic and poison livestock, foraging experts said.

Johnsongrass, a coarse green weed with a purplish hue that grows in the summer across two-thirds of the state, can be found in many Arkansas pastures and can become poisonous during changing weather conditions, such as after a drought or frost. Johnsongrass can create prussic acid - a type of cyanide gas. Other plants such as Dallis grass can also become infected with a neurological fungus.

“We have seen more [exposure] this year than in other years because of cooler temperatures and moisture content,” said Rocky Lemus, forage expert for Mississippi State University. “But ranchers don’t need to be worried; they need to be aware.”

Tom Troxel, associate head of animal science for the University of Arkansas Division of Agriculture, said that after conducting informal surveys with county agents, he counted almost 100 head of cattle lost last year because of prussic acid poisoning.

The frost wilts johnsongrass, which causes it to release prussic acid.

“When we get lower temperatures, the plant reacts to the cooler temperature and produces cyanide gas,” Lemus said.

Too much prussic acid will kill cattle outright and without warning, said John Jennings, forage expert from the University of Arkansas.

Lemus suggested removing livestock from a pasture with johnsongrass for seven to 10 days before allowing them to resume grazing, which will be ample time for the acid to dissipate.

Dallis grass’s toxicity is not from the grass but from a fungus inside the head of the flower. The seeds inside the seed head become infected with ergot, which is a neutralized fungus. The fungus lives in the soil and during the summer it germinates and creates spores that infect the Dallis grass flower. When the seed heads mature, the fungus turns brown. Honeydew, a type of sticky sap, is formed from the ergot fungus.

“Cattle have a habit of eating the seed head first and they get a super high dose of ergot and that’s when we see serious issues,” Jennings said. “It’s most commonly a case when cattle is turned on to a fresh field or there is new cattle.”

Ergot poisoning causes neurological symptoms that include trembling, staggering, delirium, convulsions or lameness.

“If they get too much of the fungus it gets to where they can’t eat or drink,” said Arkansas State Veterinarian Pat Badley. “If you find them in time and get them off the Dallis grass, they will recover.”

Jennings said that to reduce exposure to Dallis grass, mow pastures on a high setting before allowing the livestock to graze.

According to a report by the Cooperative Extension Service, there are numerous toxic plants that livestock graze and often are ingested without ill effects, but in certain conditions some plants cause greater hazards than others.

Business, Pages 25 on 10/09/2013

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