Plants Poisonous to Livestock

Introduction

Recognition of poisonous plants and the proper management of animals and pastures will help to minimize the potential for poisoning animals from poisonous plants.

When an animal goes off feed, loses weight or appears unhealthy, poisonous plants may be the cause. Poisonous plants contain toxic compounds which can injure animals. Some contain compounds that can kill, even in small doses. Others contain substances which cause a reduction in performance, such as weight loss, weakness, rapid pulse and unthriftiness. Poisonous plants should be given consideration as the potential cause, especially if the following situations exist.

1. Forage supply in a pasture is sparse due to overgrazing, drought or poor early season growth.
2. Animals have recently been 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 that an animal normally would not touch, become a potential source of food and a potential source for poisoning, just because the animal is hungry and in search of food.

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

In Minnesota, the number one cause of poisoning in cattle is nitrate poisoning. Nitrates accumulate in certain plants when grown under drought stress and/or have been fertilized with nitrogen. The crops sorghum-sudangrass and corn and the weeds redroot pigweed and common lamb's-quarters cause much of the nitrate poisoning. Sorghum-sudangrass hybrids have been the number one cause of nitrate poisoning in Minnesota.

The 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 by 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.

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

In horses, the number one poisoning problem has been from maple tree leaves. During 1988-1989, 12 to 15 cases of horse poisoning occurred in Minnesota. The plants which rank next in poisoning of horses are hoary alyssum and white snakeroot. Hoary alyssum, when greater than 30% of the feed source has 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.

The key to avoiding problems with poisonous plants is proper identification and avoidance of these plants. 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. Animals, under conditions of adequate feed, will avoid most poisonous plants. However, when feed is short, or animals are hungry, plants normally avoided become a tempting source of feed, thus a potential poisoning problem.

This bulletin identifies and describes many of the poisonous plants in Minnesota. It describes their appearance, where they grow, the parts of the plant that are poisonous and when the are most poisonous. It also describes poisoning symptoms and names some of the toxic compounds present in the plant. Knowing how to correctly identify poisonous plants will help prevent potential problems and perhaps death of an animal. Other management tips to avoid problems include:

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

Table 1 contains information to help you identify poisonous plants and help you recognize signs of poisonings.

Table 2 lists other references that may also be helpful in identification and control of poisonous plants.

Glossary

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