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College of Food, Agricultural, and Environmental Sciences


Under Dry Conditions, Toxic Plants May Attract Livestock

July 3, 2007

COLUMBUS, Ohio -- What green foliage that is thriving in Ohio's moisture-starved pasturelands may not necessarily be healthy for the livestock feeding on it.

Steve Boyles, an Ohio State University Extension beef specialist, encourages producers to be mindful of weeds and ornamentals that could be toxic to livestock. If eaten in large enough quantities, such plants can cause illnesses or can even be fatal.

"Cattle normally don't bother with weeds or other non-forage species when there is enough grass available to graze in a pasture," said Boyles. "But during drought conditions, when weeds are the only thing green still standing, they are more desirable for cattle." Because of on-going hot, dry conditions, cool-season pastureland grasses are becoming dormant and may no longer be viable forage for livestock. As a result, livestock may turn to weeds or potentially toxic plants for their salt, mineral and nutrient needs.

"Producers should get to know some of the more common toxic weeds and plants and keep livestock well fed to ensure they would not be tempted to eat them," said Boyles. "One of the biggest concerns is the risk of cyanide poisoning."

The symptoms of cyanide poisoning include labored breathing, staggering, trembling muscles and convulsions. Sources of cyanide poisoning include twigs and leaves of wild and cultivated cherry trees and certain marsh grasses, such as arrowgrass. The grass contains a high salt content that may be attractive to livestock.

A more dangerous source of cyanide poisoning is found in forage grasses, such as sorghum, sudangrasses and sorghum-sudangrass crosses. Boyles said the grasses produce prussic acid that, under dry conditions, can accumulate in high levels. The active component of the poison is hydrocyanic acid, which is extremely toxic to livestock, especially cattle and sheep.

Boyles recommends producers follow the suggested guidelines when grazing sorghum and sudangrass varieties:

• Plant sudangrass and sudangrass hybrids instead of sorghum varieties, since sudangrass hybrids have lower prussic acid potential.

• Do not graze sheep on sudangrass or hybrids until the plants are 12 inches to 15 inches tall; 18 inches to 24 inches tall for cattle.

• Do not graze sorghum-sudangrass hybrids until the plants are at least 24 inches tall.

• Re-growth sorghum should not be grazed until after the plant is completely killed by frost or dried. Young, re-growth forage can be very toxic.

• Do not graze forage varieties after a drought, or if the plants show visible signs of moisture stress. Test the plants for toxicity levels before grazing.

• Do not graze hungry livestock on forage varieties. The more they consume the greater the risk of being poisoned. It is much safer to offer feed such as hay or silage. In the case of silage, it should be allowed to ferment for at least two weeks before it is fed.

Other toxic plants include holly, rhubarb, ivy, morning glory and brackenfern.

Producers can minimize livestock illness from poisonous plants by following the suggested guidelines:

• Learn the identification of poisonous plants.

• Do not manage forage in high-density areas of poisonous plants.

• Supplement feed with salt, minerals and other nutrients.

• Avoid grazing animals in areas of abundant poisonous plants.

• Provide adequate water to prevent nonselective grazing.

To learn more about toxic plants, refer to OSU Extension Bulletin 762-00 at Information on prussic acid poisoning can be obtained through an Ohio State Extension fact sheet titled, "Livestock and Prussic Acid Poisoning" at For additional information on managing livestock under drought conditions, log on to OSU Extension's Beef Team drought information Web site at

Candace Pollock
Steve Boyles