POISONOUS PLANTS COMMONLY FOUND IN HORSE PASTURES
Dr. Krishona Martinson, University of Minnesota eXtension
Each year numerous horses (and other livestock) are injured or die as a result of accidentally ingesting poisonous plants. Recent wide-spread drought has exacerbated the problem, and many horse owners and hay producers are simply unaware of the potential injury from poisonous plants. The key to preventing problems with poisonous plants is proper identification and avoidance of these plants. 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, and look for these plants in new areas planned for grazing or haying. Horses, under conditions of adequate feed, will avoid most poisonous plants. However, when feed is short or horses are hungry, plants normally avoided become a tempting source of feed, thus a potential poisoning problem.
When a horse goes off feed, loses weight, colics, or appears unhealthy, poisonous plants may be the cause. Poisonous plants contain toxic compounds which can injure or kill (even in small doses) a horse. Others plants contain substances which cause a reduction in performance, such as weight loss, weakness, rapid pulse, or recumbency. Poisonous plants should be considered as the potential cause of disease, especially if the following situations exist:
Forage supply in a pasture is sparse due to overgrazing, drought, or poor early season growth.
Animals have recently been moved into a new pasture.
Animals have been released into a new pasture when hungry.
Herbicides have recently been used to control weeds.
Pasture has recently been fertilized with nitrogen.
A new forage source (i.e. hay or pasture) has been fed.
Below is a list of poisonous plants that are commonly found in pastures. Click here for photographs to aid in identification.
Buttercup is a yellow flowered annual or biennial that is toxic when eaten fresh in pastures. Clinical sings generally include blistering of the mouth, skin, and digestive system.
Foxtail is an annual grass. While the actual grass or vegetative parts of the plants are not harmful or toxic, the grass seed head is considered a mouth irritant. Horses may get painful blisters or ulcers on their lips or mouth after ingesting foxtail seed heads.
White snakeroot is a perennial with white flowers that only grows in shady areas and is toxic when eaten fresh and when dried in hay. White snakeroot is deadly in small doses and horses may die one to two days after ingesting it. Horses develop difficulty swallowing, muscle trembling, and have a characteristic basewide stance with their head held close to the ground.
Wild parsnip is a yellow flowered biennial that is toxic when eat fresh or when dried in hay. Severe sunburn (photosensitivity) occurs in horses (other livestock and humans as well) ingesting wild parsnip if they are exposed to UV light after ingestion. Severe sunburn is reduced if the livestock are shaded from the ultraviolet sunlight.
Waterhemlock is a perennial with white flowers that is found in wet areas or along streams. The root of waterhemlock is toxic, even in very small amounts. Animals are commonly found dead after ingestion of waterhemlock.
Hoary alyssum is a short lived perennial with a small white flower that is commonly found pastures and hay fields. Hoary alyssum is toxic when eaten fresh and when dried in hay. Most horses react differently to hoary alyssum toxicity. Signs are usually observed 12 to 24 hours after the horse ingests hoary alyssum and include swelling of the lower legs commonly referred to as “stocking up”.
Some herbicides may increase the palatability of these weeds. Therefore, it is important to read the herbicide label and follow all grazing restrictions (all herbicides have grazing and harvest restrictions). Also, if there are poisonous plants in the pasture, it is best to keep all livestock out until the plants have died and the grazing restriction has passed.
Other poisonous plants to be aware of (in both hay and/or pasture) include:
Mold Infested Clovers
Black Walnut Shavings
Common Cocklebur (seedling)
Acorns (green or immature)
Weed Seeds (in grain or oats)
Endophyte Infested Fescue
Maple (dried or wilted leaves)
Websites related to Poisonous Plants: