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Plants poisonous to livestock

Recognizing poisonous plants and properly managing animals and pastures will help minimize the potential of poisoning animals. When an animal goes off feed, loses weight or appears unhealthy, poisonous plants may be the cause.

Poisonous plants contain toxic compounds that can injure animals. Some contain compounds that can kill, even in small doses. Others contain substances that reduce performance, such as weight loss, weakness and rapid pulse.

Signs of poisoning

Consider poisonous plants as the potential cause, especially if the following situations exist:

  1. Pasture forage supply is sparse due to overgrazing, drought or poor early-season growth.
  2. Animals recently moved into a new pasture.
  3. Animals have been released into a new pasture when hungry.
  4. Herbicides have been used to control weeds.
  5. Pasture has recently been fertilized with nitrogen.
  6. A new forage source has been fed.

Most poisonings occur in the early spring or during a drought when feed is short. Plants an animal normally wouldn’t touch become a potential source of food and a potential source for poisoning, just because the animal is hungry and searching for food.

Also, some herbicides may increase the palatability of some weeds. This is why it’s important to read the herbicide label and follow all grazing restrictions. Also, if there are poisonous plants in the pasture, it’s best to keep all livestock out until the plants have died.

Poisoning in different livestock

Poisoning in cattle

In Minnesota, nitrate poisoning is the number one cause of poisoning in cattle. Nitrates accumulate in certain plants when grown under drought stress or they’ve been fertilized with nitrogen.


Much of the nitrate poisoning is caused by the crops sorghum-sudangrass and corn, and the weeds redroot pigweed and common lambsquarters. Sorghum-sudangrass hybrids have been the number one cause of nitrate poisoning in Minnesota.

Other main causes for cattle poisoning in Minnesota rank as follows:

  1. Gallotannins in oak species, mainly in southeastern Minnesota.
  2. Cyanide poisoning caused by sorghum species and chokecherry plants.
  3. Glycoside poisoning from nightshades and cocklebur.
  4. Photosensitive skin reactions from St. Johnswort and buckwheat.
  5. Cicutoxin poisoning from water hemlock.
  6. Alkaloid poisoning from poison hemlock.

Poisoning in sheep

The top two causes of plant poisonings in sheep in Minnesota have been nitrates poisoning and photosensitive reactions.

Poisoning in horses

In horses, wilted maple tree leaves are the number one poisoning problem. 

Hoary alyssum and white snakeroot are the next highest-ranking plants in terms of poisoning horses. When hoary alyssum is more than 30 percent of the feed source, it’s been linked to stocking up (swelling of the lower legs) and other problems in horses. White snakeroot has caused death.

Other less common plants causing livestock poisonings are water hemlock, poison hemlock, brackenfern and the nightshades.

Strategies for preventing poisoning

Identify poisonous plants

The key to avoiding problems with poisonous plants is to properly identify these plants and avoid them. Become familiar with the plants that can cause problems. Examine pastures, hay fields, roadsides and fence rows for poisonous plants.

In a drought year or a year when feed is short, take extra precautions to look over new areas planned for grazing or haying such as roadsides, wooded areas or sloughs.

When animals have adequate feed, they’ll avoid most poisonous plants. However, when feed is short or animals are hungry, plants normally avoided become a tempting source of feed and a potential poisoning problem.

Manage pastures

Knowing how to correctly identify poisonous plants will help prevent potential problems and perhaps an animal’s death. Other management tips to avoid problems include:

  • Avoid overgrazing pastures.
  • Avoid turning hungry animals into new pastures.
  • Learn to identify poisonous plants.
  • Fence off areas in pastures where poisonous plants occur.
  • Control or manage plants to avoid poisoning problems.
  • Follow herbicide grazing restrictions.
  • Rotate pastures to prevent overgrazing.
  • Supply adequate supplies of clean, fresh water for livestock.
  • Consult your veterinarian to correctly identify a suspected poisoning from plants, to prevent it from happening in the future.


Poisonous plants

The following are descriptions of many of the poisonous plants in Minnesota. We’ll describe what they look like, where they grow, their poisonous parts and when they’re most poisonous. In addition, you’ll find information about poisoning symptoms and some of the plant’s toxic compounds.


Authors: Lisa M. Behnken, Extension educator and Beverly R. Durgan, Extension Dean and weed scientist

Reviewed in 2023

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