A List of Poisonous Plants to Horses

This is a list of poisonous plants to horses. It includes some of the most common weeds which could affect grazing horses.

It is unlikely that any pasture is completely void of all poisonous plants. However, due to the unpalatable condition of many toxic weeds and the quantities a large animal would have to consume of the poison for its size, the likely hood of an adverse reaction is rare. However, an awareness of the poisonous plants to horses is important when it comes to your equine’s health.

There are some weeds however, which are very toxic and can lead quickly to serious illness and death. These plants are best known by sight so you can ensure that your equine doesn’t have access to them while grazing or where you may ride.

Generally, poisonous plants are broad leaved plants that are hardy under stressful conditions such as drought or over grazing. Keep pastures groomed as mowing minimizes the ability of the broad leaved plants to grow and spread.

The List...,

This is a partial and on going list of the poisonous weeds and plants which may be found in your horse's pasture.

Poisonous plants to horses: Fiddlenecks
Name: Amsinchkia Intermerdia
Location: pastures and roadsides, you can find this as a common contaminant of untreated grain crops, some hay and first cuttings of alfalfa
Description:Annual plant with yellow or orange flowers. Stems are single or branched with dark to grayish green hairy leaves.
Symptoms: Seeds are considered the most toxic part of this plant. Contaminated grain or hay has been a source of the past. They are a plant which can be highly poisonous to horses.

Poisonous plants to horses: Poison Hemlock
Name: Conium Maculatum
Location: road sides, dry ditches
Description:Multistemmed perennial weed with toothed leaves with clusters of small white flowers. The stems have purple spots. Stems and seeds contain potent neurotoxins that affect the nervous system. A small 4-5 pounds is a lethal dose for a horse.
Symptoms: From uneasiness to death within 18 minutes. Includes the grating of teeth, clamping of jaw and pain.

Poisonous plants to horses: Water Hemlock
Name: Cicuta Maculata
Location: wet pastures or ditches, water sides
Description:A perennial weed with erect hairless stems and fleshy roots. Water hemlock is considered one of the MOST TOXIC plants and all parts of the plants contain an alkaloid which affects the nervous sytem, but toxins are mostly concentrated in the root. Less than 1 pound of leaves can be fatal. Toxin levels diminish as the plant matures.
Symptoms: From uneasiness to death within 18 minutes. Includes the grating of teeth, clamping of jaw and pain.

Poisonous plants to horses: Bracken Fern
Name: Pteridium Aquilinum
Location: open fields, dry ground, rocky soil
Description: Perennial fern with triangular leaves that can reach 2-3 feet in height. Inhibits the absorption of vitamin B1 which is necessary for nerve function and neurological soundness. Toxicity levels in leaves are low.
Symptoms: Slow to develop is jaundice, weakness, staggering gait, depression, drooling, hemorrhaging from nostrils, blood in urine and feces, loss of appetite.

Poisonous plants to horses: Horsetail
Name: Equisetum Arvense
Location: poorly drained, sandy, acid soils or cultivated fields or roadsides or woods.
Symptoms: Slow to develop is jaundice, weakness, staggering gait and excitability to paralysis.

Poisonous plants to horses: Tall Buttercup
Name: Ranunculus Acris
Location: pasture, meadows, roadsides
Symptoms: Inflammation and blisters where the plant’s juices touched the animal, drooling, loss of appetite.

Poisonous plants to horses: Lupine
Name: Lupinus Polyphyllus
Location: pasture, meadow, roadsides
Symptoms: Nervousness, labored breathing, aimless running, convulsions

Poisonous plants to horses: Saint John’s Wort
Name: Hypericum Perforatum
Location: pastures and roadsides
Symptoms: Photosensitivity, tongue and mouth

Poisonous plants to horses: Nightshade
Name: Solanum sp.
Location: open dry woods, cultivated fields, pastures, farm yards
Symptoms: Abdominal pain, diarrhea, loss of muscular coordination, dilation of pupils, death

Poisonous plants to horses: Jimsonweed
Name: Datura Stramonium
Location: cultivated fields and farm yards
Symptoms: Fast / weak pulse, nausea, loss of muscular coordination, aggressive behaviours, trembling, impaired vision

Poisonous plants to horses: Milkweed
Name: Asclepias sp.
Location: dry open areas, pastures, roadsides, woods
Symptoms: Loss of appetite, constipation, persistent colic, drooling, breathing issues, convulsions, death.

Poisonous plants to horses: Cockle
Name: Saponaria Officinalis
Location: pastures, cultivated fieds, roadsides
Symptoms: Restlessness, teeth grinding, drooling, colic, weak pulse to coma to death.

Poisonous plants to horses: Cocklebur
Name: Xanthium Chinensis
Location: cultivated fields, stream banks, farm yards
Symptoms: Symptoms appear within a few hours, unsteady gait, neck muscle twisting, nausea, rapid weak pulse, death.

Poisonous plants to horses: Tansy Ragwort
Name: Senecio sp.
Location: pastures, hayfields
Description: about 70 species grow in different habitats. Toxicity varies across the species, and some may include alkaloids which inhibit cell division especially in the liver. Damage can be irreversible.
Symptoms: Chills, high temperature, staggering gait, weakness, loss of coat luster, rapid pulse.

Poisonous plants to horses: Spurge
Name: Euphorbia sp.
Location: roadsides, cultivated fields
Symptoms: Contact with sap causes inflammation of skin; eating causes diarrhea, vomiting, stomach pain, sweating, muscle tremors.

Poisonous plants to horses: White Snakeroot
Name: Eupatorium Rugosum
Location: wooded areas, stream banks
Symptoms: Excessive salivation, nasal discharge, depression

Poisonous plants to horses: Sneezeweed
Name: Helenium automnale
Location: wet areas, roadside ditches, stream banks
Symptoms: Slow to develop the symptoms include loss of vigor, muscular control, drooling, high temperature, dizziness, convulsion, labored breathing.

Poisonous plants to horses: Johnsongrass / Sudan grass
Name: Sorghum spp.
Location: roadways and uncultivated areas
Description: Leaves contain a cyanide compound which can inhibit the body to absorb oxygen. Circumstances which injure the plant such as trampling, frost or wilting can chemically liberate the cyanide making them toxic to grazing animals. Cyanide concentration drops to safe levels when the grasses are cured for hay but nitrates if present do not.
Symptoms: rapid breathing, tremors, urination, gasping, convultions

Poisonous plants to horses: Crazyweed
Name: Astragalus spp or Oxytropis spp
Location: dry sandy soil
Description: Leafy perennial with short stem and tuft like leaves. Contains a alkaloid which inhibits the production of enzymes and disrupts the function of the brain cells.
Symptoms: head bobbing, exaggerated steps, staggering, fall. Excessive poisoning is irreversible.

Poisonous plants to horses: Rose Laurel
Name: Nerium Oleander
Location: landscapes
Description: An evergreen shrub. Thick leathery leaves with flowers white, pink or red. Leaves are toxic and can see effects several hours after ingestion.
Symptoms: colic, difficulty of breathing, tremors, irregular heart.

Poisonous plants to horses: Red Maple Tree
Name: Acer Rubrum
Location: landscapes
Description: Medium sized tree that has leaves which turn bright red in fall. Ingestion of fresh growing leaves causes little to no harm, however, as the leaves wilt they become extremely toxic. Toxins in wilted leaves cause red blood cells to break down so that the blood can no longer carry oxygen. Small amounts of leaves (approximately 1-4 pounds) can be fatal.
Symptoms: in a few hours you may see pale yellow gums, increased repiratory rate, rapid heart rate, dehydration.

Information on plants which are poisonous to horses

Article: Is Your Horse's Pasture Toxic?

PLEASE NOTE: This web page is based on the research and conversations that we have had with various people and professionals on the subject of horses health and horse wormer requirements and is not intended to replace veterinary care for your animals. We do not accept liability for errors or omissions. A vet, horse nutritionist or other trained professional should always be consulted with any equine concerns, or before changing any feeding or care regime.