Preventing Plant Poisoning

Alexa Linton, Equine Sport Therapist, BSc. Kin

Published in Island Horse Magazine

It happens far too often. A horse with nothing better to do and nothing better to eat, snacks on a plant which is harmful or possibly even fatal. Confusion and chaos often ensues, with the horse displaying distressing symptoms, sometimes within hours of ingestion, other times weeks after ingestion. When it comes to poisonous plants the most susceptible horse is one that is not used to grazing, and is not able to discern between good plants and bad plants, or one who does not have adequate forage to eat and is hungry enough to eat something which is harmful.

It is a horse owner’s worst nightmare. The horse is suddenly frothing at the mouth, neurologically impaired, displaying colic-like symptoms, or dead lame for no apparent reason. Help is called, but it is difficult to know what happened to cause such severe symptoms. In the worst cases, there is no time to find out.

As a horse owner, it is our responsibility to be knowledgeable about plants and other environmental hazards that can be harmful to our horses. Although many horses can recover from such toxicity, many plants have a cumulative effect, with symptoms only manifesting when the effects of the plant toxin are terminal, in other words when they are very difficult to reverse.

Fear and avoidance of grazing are not the intention of this article, as grazing is a natural and healthful process for a horse, and those horses who graze regularly gain a distinct knowledge of plants that are healthy and those that are not. Rather, the emphasis is on becoming educated on what is growing in your pasture and working to prevent problems and implement solutions. It is important to remember as well that the hay we are feeding our horses may contain harmful plants, which can be easily removed after a quick check.

It is common sense that a horse who is grazing in a pasture with very little grass and an abundance of other green plants (including those which are poisonous), will eat whatever they can get their teeth on. The first step towards a safe pasture is ensuring there is always sufficient grass or hay for the horses to eat. This prevents them from eating other plants out of boredom or hunger. The second step and most important step is learning about the plants that can be harmful to your horse and removing them from your pasture and from your hay.

Horse-Harmful Plants on Vancouver Island

On Vancouver Island, as in any place, there are horse-harmful plants that grow in abundance and others that are rarely found. Refer to the web resources below for the best method of removal for each plant. Today we will outline the plants that tend to be the most prevalent in our own backyard.

Alsike Clover – One type of common clover, alsike clover can be distinguished by the flower stem, as it originates from the same point on the stem as the separate leaflets. The most common symptom of alsike clover toxicity is photosensitivity or reaction to sunlight, but the real problem is gradual liver damage. On darker horses, photosensitivity often goes unnoticed, but can present as nervousness, inflammation or lesions of muzzle, eyes, ears or mouth, digestive disorders, and brownish urine. If toxicity is suspected, remove horse from affected pasture. It is also recommended by the Ministry of Agriculture that alsike clover be removed using specific herbicides.

Bracken Fern – This common plant is typically found in barren pastures and woodlands and is recognized by its triangular fronds. Over a period of one to two months ingestion causes a vitamin B1 deficiency that can lead to weight loss, muscle tremors, and death. Horses may develop a taste for this plant and prefer it over other forage. This plant is also toxic when found in hay and other baled forage. Symptoms can be reversed with daily injections of vitamin B1 for 2 weeks.

Buttercups – A highly recognizable plant because of its yellow flowers, buttercup can cause inflammation and trauma to the gastrointestinal tract. It tends to be self-limiting, as the horse will often develop sores in the mouth and it will be too painful to eat, but a visit from the veterinarian is recommended.

Poison Hemlock – One of the most well-known poisonous plants, Poison Hemlock commonly grows in roadside ditches and waterways. It is possible to for death to occur in a horse in less than 15 minutes. Symptoms include frothy mouth, dilated pupils, convulsions, and a weak, rapid pulse. If ingestion is suspected consult a veterinarian immediately.

St. John’s Wort – This plant with large yellow flowers can be found in pastures, roadsides, and water areas. Ingestion can cause photosensitization, which may result in horse becoming sunburned or blistered under normal sunlight. Avoid grazing in areas where this plant is abundant.

Oak – Poisoning by oak tends to be seasonal, with horses eating the new leaves in the spring and acorns in autumn. Eating small amounts of leaves or acorns is relatively harmless, but many horses enjoy the taste of acorns and actively seek them out. Also, horses tend to have different levels of tolerance to the oak plant.

Oleander – With its beautiful white flowers, oleander ranks with yew in terms of toxicity. In fact, one ounce of oleander leaves can kill a 1,000lb horse. Symptoms include sweating, colic, difficulty breathing, and arrhythmia. If a less than lethal dose is ingested, symptoms may be reversed with the help of a veterinarian.

Rhododendron - This perennial shrub is a common favourite in Vancouver Island gardens because of its beautifully coloured flowers. Within six hours of ingestion a horse can appear colicky, with tremors. If enough of the plant if ingested, toxicity can be fatal. .

Tansy Ragwort – This plant is best recognized by its bright yellow flowers which bloom from July to October. It is found throughout North America in pastures, hayfields, and on roadsides. Symptoms include incoordination, liver failure, and high temperature. If ingestion is suspected consult a veterinarian immediately.

Yew – All parts of the yew tree (branches/leaves/berries) are extremely toxic to horses and other grazing animals. As little as one mouthful of Japanese yew can result in death, usually with no warning. Be sure to block off any areas of pasture which have access to a yew tree.

Horsetail – This common plant is found in poorly drained soils, as well as sandy, gravel soils. It is often found in hay and may be more toxic in this form. Symptoms are often slow to develop and include loss of appetite, weakness, paralysis and staggering gait.

There are many other plants that can also have a toxic effect on horses, but it would take most of the magazine to list them all. Google “Poisonous plants for horses” for a host of informative websites.

The best way to work with horse-harmful plants is prevention! Be pro-active in your horse’s health and well-being by referring to this article and the following resources and removing poisonous plants from your pasture.

Alsike Clover Toxicity in Horses

http://www.agf.gov.bc.ca/forage/alsike/alsike.htm

Ministry of Agriculture – Weed Management

http://www.al.gov.bc.ca/cropprot/weeds.htm

Poisonous Plants – A primer to keep your horse safe

http://www.raspberryridge.com/Feature-Poisonous%20plants.htm

If you do suspect your horse has had an encounter with a poisonous plant, it is worthwhile researching complementary healing methods to work alongside immediate veterinary intervention. This can assist in the recovery from toxicity and help your horse get back on track.