Some vines, broadleaf plants and wildflowers may be poisonous to horses and many of these poisonous plants are commonly found in pastures. Horses frequently graze in pastures that are riddled with toxic plants although most poisonous plants do not present a threat to horses. Horses will find the plants unpalatable and prefer quality forage. Also, most full grown horses weigh from 800 to 1,000 pounds or more. The overall size of a full grown horse would generally require a large meal of toxic plants to cause concern, with only a few exceptions. Owners may ease anxiety by occasionally browsing pastures to eliminate dangerous weeds, like the ones noted below, that may be toxic.
Bracken fern is a common plant that may be found in woodlands and moist open areas in most states in America. Some horses develop a taste for bracken fern. The fern has triangular shaped leaves that can grow from two to three feet high in clumps. Once ingested, the fern can impede the absorption of thiamin and inadequate amounts of thiamin in a horse's system may lead to neurological impairment and even blindness. Treatment for bracken fern consumption is large doses of thiamin over a couple of weeks under the supervision of a veterinarian.
Hemlock is a multi-stemmed perennial weed with clusters of small white flowers; purple spots may be seen near the base of the stem of the plant. The weed grows throughout North America. Small doses of the stems or seeds may affect the nervous system of a horse resulting in respiratory failure. Horses will generally avoid hemlock and may recover from small doses. However, there is no known treatment for hemlock ingestion.
Johnsongrass is native to southern climates. It is a coarse grass with a seeded head that may grow up to six feet in height. A cyanide compound may be found in the leaves and stems of johnsongrass. The highest concentrations of toxins are located in young shoots of the plant. Adult plants are not likely to cause illness due to the metabolism of a horse. Frost, trampling and wilting may release the cyanide in the plant and render the plant dangerous. The cyanide levels drop when cured for hay. Signs of cyanide poisoning are rapid breathing, tremors and convulsions.
An evergreen shrub, known as oleander, is bountiful in the southern United States. The shrub has white, pink or red flowers which grow in clusters and thick leathery leaves. The shrub may grow as large as a small tree. Toxins found in the plant may disrupt the heartbeat. Indications of ingestion include shallow breathing, colic, tremors, fast or slow pulse and an irregular heart rate. The effects generally wear off after 24 hours. Charcoal should be administered and an anti-arrhythmic drug to stabilize the heart under the supervision of a veterinarian.
There are many other weeds commonly located in pastures that are unsafe for horse consumption. Veterinarians, other horse owners, trainers and the internet are good sources of information concerning poisonous weeds. The metabolism, taste buds and overall size of a horse will protect most horses from consuming dangerous plants but owners can lessen the odds of accidental consumption by practicing good pasture management.
Photo courtesy of Horse Grazing as uploaded by Neil Williamson on Flickr’s Creative Commons.
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