Poison Pastures: Guide To Flowers and Plants Harmful to Horses
Although horses usually graze freely when they are out in open fields, there are a number of plants and flowers that are very harmful to them. Some of these can even be poisonous, so it is very important to make sure that the pasture area is free from these types of plants. When horses consume poisonous plants, the effects can range from vomiting, lesions, depression, paralysis and even death. Study the resources below to learn more about which plants are dangerous for horses, and make sure to thoroughly and frequently inspect any fields or open areas where your horses are allowed to roam freely.
- Yew – Yew trees are evergreens with distinct bell-shaped pink flowers. The alkyloids in the plant affect the natural functioning of the horse’s heart. Even a mouthful of yew from any part of the plant can cause horses to experience digestive illness and quick death.
- Oleander – Oleander is commonly found in woods and is also used as an ornamental garden flower. It is highly toxic to horses and a small amount can cause extreme discomfort, sweating and breathing difficulties. An ounce or more can cause death.
- Yellow Star Thistle – Yellow star thistle is actually a weed featuring a bright yellow flower. It typically grows in warm, dry areas and flowers in the winter months. Yellow star thistle initially affects the mouth and tongue of horses, causing swelling so that the horse cannot swallow. Its toxins also affect the brain permanently and there is usually no recovery.
- Locoweed – Locoweed is a plant that grows year-round, usually in dry areas such as the Rocky Mountains. It grows low to the ground, with blue, purple or red blossoms. Live plants are extremely toxic, while dried or dead plants are less toxic. If dried plants are ingested, the symptoms of poisoning may not occur until a few weeks later. In the case of fresh plants, vision and perception would be quickly affected, and neurological impairment would also occur. It can also bring on miscarriage in pregnant horses or infertility in males. Even horses that do recover would not typically return back to normal.
- Timber Milk Vetch – Timber milk-vetch is usually found along the mid to western states. It is a very toxic herb that causes poisoning in livestock, other animals and even bees. Its general signs of poisoning are breathing difficulties, coordination problems, and death within a few days if left untreated.
- Lupine – The poisonous species of lupine grows as a perennial in wooded or mountainous regions, especially during spring in wet weather. The plant can be up to a meter tall, with small clusters of leaves and colorful flowers. If a horse consumes more than half a kilogram of lupine, it could experience convulsions or twitching, anxiety, difficulty in breathing and moving, coma and death.
- Poison Hemlock – Hemlock grows widely in most parts of the U.S., especially in wet areas. They can grow up to several feet high and feature small leaves with white flowers at the top. Within a couple of hours of eating poison hemlock, a horse would usually show extreme anxiety and coordination difficulty, trembling and colic. If it doesn’t recover within a few days, it could become paralyzed and then die. Horses that consume a few pounds of poison hemlock would die within a few hours.
- Water Hemlock – Water hemlock looks quite similar to poison hemlock and even grows in the same areas, but can be identified by the pungent yellow sap it emits when cut. The roots are the most toxic part and a couple of ounces could cause death in horses. In less severe cases, the horse would experience uncontrolled salivation, convulsions, failure of the muscles and heart and breathing problems.
- Ground Ivy – Ground ivy is a low-growing herb with tiny, distinctive blue flowers. It grows in wet shady areas, such as fields, gardens, and farmlands. While animals usually avoid ground ivy for its unpalatable taste, it can sometimes be unintentionally mixed in their hay. When ingested in large quantities, ground ivy can cause horses to sweat and salivate excessively and breathe heavily, but it rarely causes death.
- Larkspur (Delphinium) – Larkspurs, a perennial herb, are related to the buttercup family and they can be recognized by their pretty clusters of bright, hanging purple or blue flowers. Eating this plant can cause horses to experience paralysis, asphyxiation and eventually death.
- Bracken Fern – Bracken fern grows as a perennial herb, with large, wide leaves. It grows throughout the U.S., usually in dry woodland areas. All parts of the plant are toxic to horses and can cause an acute deficiency of thiamine in their bodies. The symptoms of its poisoning include listlessness, coordination loss, and a lowered heart rate.
- Horsetail – Horsetail primarily grows in soils that contain plenty of sand or gravel, as well as in fields containing crops. Young horses are more susceptible to its toxic effects. Horsetail is more toxic in its dried form (for example, mixed in hay) than fresh. It causes jaundice, muscle weakness, nervousness, appetite loss and sometimes also paralysis. There is currently no treatment for the effects of horsetail.
- Castor Bean Poisoning – Castor bean plants showcase wide leaves with eight leaflets. Its flowers are usually small and green, while the fruit are colorful and spiny. The seeds, sap and leaves are dangerous for horses. Even a tiny amount has been proven to be far more deadly than a rattlesnake’s venom. A few milligrams can cause vomiting, convulsions and death in horses.
- Red Maple – Red maple trees feature green leaves for much of the year that turn a distinctive bright red color in fall. While the leaves are still green, horses can usually safely eat them with no ill effects. When the leaves turn red, a few ounces can cause jaundice, strained breathing, and colic. This is due to a mass attack on the animal’s red blood cells by a chemical in the leaves.
- Buckwheat – Buckwheat is a broad-leafed plant featuring tiny white flowers and brown seeds in a triangular shape. It grows widely through the U.S., often grown as a crop, but sometimes also as a weed along roads. The entire plant is toxic for horses and it causes photosensitivity (sensitivity to light). Symptoms would include digestive trouble, skin rash or inflammation, and a sudden urge to escape sunlight.
- Rhododendrons and relatives – Rhododendrons grow in large amounts in the eastern states. They grow as shrubs or trees, with clusters of colorful flowers. Toxins in the nectar and pollen of the flowers, as well as other parts can cause pain and irritation in the stomach, changed heart rates, convulsions and death.
- Potato and Tobacco Leaf Poisoning – Parts of the potato and tobacco plants, especially the leaves are very toxic for horses. Consuming them could cause damage to the heart and stomach, as well as death if a large amount has been eaten. Green potatoes or potato buds produce similar symptoms when consumed.
- Fiddleneck and related plants – Fiddlenecks are annual low-lying plants with broad leaves and small flowers. Large amounts can cause severe liver damage, weight loss, jaundice, confusion and other neurological problems. The symptoms can continue for about a week.
- Crotalaria Species – Plants in the Crotalaria species grow as shrubs, especially through the southeastern states. It features small yellow flowers and seed pods that rattle when shaken. A small amount can cause horses to experience liver failure, agitation or listlessness, and even death within a few hours. On a more long term basis, the horse could show signs of weight loss and persistent sleepiness.
- Senecio Species (Tansy Ragwort) – Tansy ragwort is a tall, gangly plant with clusters of yellow flowers. It grows as a weed through the summer months and is infamous for poisoning horses and other livestock. Poisoning by this plant can result in symptoms such as agitation, appetite loss, weakness and death. It cannot be treated.
- Chokecherry and Wild Cherry (Prunus) – Chokecherry grows as a tall shrub with medium sized leaves and small, white flowers that bloom on a spike. Chokecherry and wild cherry plants contain cyanide. When consumed by horses, the animal could die between a few minutes to a couple of hours.
- Sorghum and Sudan Grass – Sorghum and sudan grass grow as long, thin plants with many leaves. While they are often used as forage for livestock, they can also cause poisoning when the growth is suddenly disturbed, such as during a frost or cutting. Prussic acid in the plant can cause horses to have trouble breathing, display symptoms of colic and have blood in their urine. Pregnant horses could miscarry and in general, the acid could cause death.
- Bermuda Grass – Bermuda grass grows abundantly in warm, sunny areas and can even survive in fairly dry soil. It can cause staggering, liver damage, photosensitivity, strained breathing, collapsing and death due to breathing problems.
- Black Locust – Black locust grows as a weed through the central and eastern areas of the U.S. It is a medium size plant, with drooping flowers and compound leaves. Horses are especially drawn to young black locust plants, but ingesting these can cause colic, kidney failure, increased heart rate and appetite loss. Eating half a pound or more could lead to death.
- Oak Trees – Oaks are large, shady trees that bear acorns. All parts of the tree, especially the acorns and new leaves are toxic for horses. It primarily affects the gastrointestinal system, causing blood in diarrhea, ulcers and kidney damage or complete failure. The horse may appear confused and weak, without an appetite.
The best way to prevent horses from poisoning is by scouring their pasture areas and immediately removing any known toxic weeds, shrubs and plants. Also make sure not to plant any trees or flowering plants that are dangerous for horses. Be especially vigilant during spring and summer when many of these plants tend to propagate. If a horse does start to show signs of poisoning or behaves strangely, don’t wait to see if it gets better in a few hours. Instead, call a vet immediately! Many of these toxic plants can bring severe illness or death within an hour or two, so it is vital to act right away.