University of Minnesota Extension
Day One: Waterhemlock
Identification: Can be two to seven feet tall, with hollow stems that are branched at the top. White flowers that are borne in umbrella shaped clusters called umbles. The roots produce a yellowish fragrant oil when cut. Leaves are toothed edges and grasps the stock like celery bunch.
Habitat: Swamps, lowlands, and along water edges
Signs and Effects: Animals are commonly found dead after ingestion of the roots. In observed cases horses showed anxiety and facial muscle twitching, seizures, and teeth grinding.
Treatment: Animals that ingest the root and survive for eight hours after the onset of clinical signs are more likely to survive. There is no specific treatment for the ingestion of Waterhemlock.
Day Two: Foxtail
Habitat: Found in recently disturbed soils and sandy areas. They can be found in pastures and hay fields after periods of drought or new seeding.
Signs and Effects: Horses that ingest the seed heads may delevope blisters or ulcers on the lips and mouth from the microscopic barbs embedding into the soft tissue. The horses may develop weight loss due to gastrointestinal tract being damaged is large amount is ingested.
Treatment: Removal of the plant and supportive of the blisters or ulcers such as rinsing with water.
Day Three: Field Horsetail
Identification: Hollow, wiry, jointed stems, whorled leaves. No flowers are produced; instead a cone like structure is at the top.
Habitat: Found in moist to wet soil, usually sandy or gravely in texture.
Signs and Effects: Horses develop depression, constipation, and unsteady gait usually one to two days after ingestion. Clinical signs progress to twitching, going down, paddling, and seizing for a period of a week or more.
Treatment: Thiamine is given for up to five days.
Day Four: Hoary Alyssum
Identification: Stems are grey-green, hairy, one to three feet tall, with many branches near the top. Flowers are white with four deeply divided petals. Seed pods are hairy, oblong and appear to be swollen with a point on the end.
Habitat: Meadows, pastures, and is a common weed in hay fields. It is also adaptable to dry conditions on sandy or gravely soil.
Signs and Effects: Clinical signs are usually noticed 12-24 hours after ingestion. Signs include edematous, swelling of the lower legs, fever of 103F or higher, warm hooves, pronounced digital pulse, stiffness of joints, reluctant to move, “camped out” stance, and very rarely death.
Treatment: Clinical signs usually resolve after two to four days with supportive treatment following removal of the weed source. It may take horses longer before returning to athletic performance.
To get the complete book of poisonous or harmful to horses in the North Central United States you can visit the University of Minnesota Extension Service.