Equine Poison Prevention
ASPCA Hazard List
The veterinarians at the ASPCA Animal Poison Control Center have compiled the following list of spring and summer hazards for horses:
- Black walnut (e.g. as shavings in bedding)
- Blister beetles, which can sometimes be found in alfalfa hay, especially in the Midwest and Southwest)
- Oak (especially new-growth leaves in the springtime)
- Rhododendron and azalea
- Taxus species (yew, Japanese yew, American yew, English yew, western yew, oleander and rose laurel
- White snakeroot, richweed, white sanicle, jimmy weed, rayless goldenrod, burrow weed
- Wilted red maple leaves
- Yellow star thistle, St. Barnaby’s thistle, Russian napweed
If you suspect that your animal has ingested a poisonous substance, please call your veterinarian or the ASPCA Animal Poison Control Center’s 24-hour hotline at 888-426-4435.
Hoary Alyssum - Threat to Horses
Hoary alyssum is an invasive weed in the mustard family. It grows in pastures, road shoulders, railroads, agricultural fields and other disturbed areas; and, prefers dry, sandy, or gravelly soils. Hoary alyssum is toxic to horses, causing swollen legs, laminitis and severe lameness. Consumption of large quantities can cause diarrhea, leading to dehydration, and can cause abortions in pregnant mares. Death may result, although most treated horses recover. The plant remains toxic after it is dried, and most poisonings are due to contaminated hay. Hoary alyssum spreads by seeds. This plant is considered a noxious weed in Michigan.
Hoary alyssum can be an annual, biennial or perennial. The tap-rooted plant emerges in early spring. It is an erect or spreading plant, growing up to three feet tall, with multiple stems arising from the base of the plant. The thin stems branch near the top of the plant, and leaves and stems are covered in whitish, star-shaped hairs. The 0 to 10 inch, gray green leaves are alternate and lance-shaped; upper leaves clasp the stem. Hoary alyssum produces small white flowers, borne in clusters at the end of the stems, from May to September. There are four petals, however, since each petal is deeply lobed, the flowers can appear to have 8 petals. The small, oblong, flattened fruit has a short beak and is often covered with star-shaped hairs.
Hoary alyssum can be controlled through mechanical and chemical means. Hand-pulling is effective on small infestations; plants should be pulled before they can go to seed. Contact the weed control board for site-specific chemical recommendations.
Information taken in part from: MSUE/Project GREEEN “Identification, Livestock Toxicity and Control of Hoary Alyssum in Christmas Tree Plantations and Forages.”