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Horses that graze the toxic hairy vetch plant are at substantial risk of developing a potentially life-ending condition known as systemic granulomatous disease (SGD), or equine sarcoidosis (ES). Systemic granulomatous is thought, in part, to stem from the ingestion of plants that are known to contain high levels of the trace-mineral selenium, such as the hairy vetch (Vicia villosa). A reddish-purple plant with hairy stems (hence the name), this annual or biennial plant grows across 50 states and in moderate climates throughout the world. It is known to accumulate large amounts of nitrogen and cyanogenic glycosides, a highly dangerous toxin found in various plants.
Horses will not consume a toxic plant such as the vetch unless under a specific set of circumstances. In cases of an over-grazed pasture or periods of drought, horses will go in search of any kind of vegetation, including those that they would otherwise avoid. Most of this vegetation, like hairy vetch (v. villosa) is poisonous; its bitter taste is only tolerated by the hungriest of horses. The nutrients needed for the horse to grow and perform will not be found in toxic plants and weeds, and a horse will progressively weaken, or experience sudden death. When supplied with plenty of nutritious feed or fresh greenery, however, horses are able to maintain the appropriate balance of vitamins and minerals needed to maintain good health.
Due to the abnormally high amount of selenium, and the possible development of systemic granulomatous disease, the vetch is among the greatest enemy of horses. The inflammatory disease manifests a few conditions in horses, including exfoliative dermatitis, anorexia and the inflammation and failure of multiple organs. A painful peeling or “shedding” of the skin is the primary component of exfoliative dermatitis. Due to progressive weakening of several organ systems, most horses ultimately succumb to Systemic granulomatous disease (SGD).
Horses that graze the toxic vetch plant are at risk of developing Systemic Granulomatous Disease (SGD), a potentially life-threatening condition characterized by exfoliative dermatitis, thickening of the skin, loss of coordination and possible death.
Vetch toxicity can be acute or chronic, and will vary in the extent of the poisoning.
In acute vetch poisonings, symptoms may include:
A chronic poisoning is characterized by:
When the horse consumes, or even just chews the vetch, digestive enzymes transform the cyanogenic glycosides into cyanide. The potential for cyanide poisoning is low, as long as the plant is consumed in small amounts, and the horse is an overall healthy adult. The high level of selenium is another matter. The vetch depends on a large bank of selenium to grow to heights of six feet, and at any point in time is harboring an amount highly toxic to livestock. These plants are known as obligate selenium accumulators, and are rooted in soil with toxic levels of the mineral.
Diagnosis will require a history of the horse, including observations of symptoms, as well as physical and behavioral changes. The veterinarian will conduct a full exam of the horse, and perform a complete blood count, a serum chemistry profile to verify protein levels, an abdominal ultrasound, and a skin biopsy to analyse the changes. Additionally, radiographs may be done to view organ involvement. Hair, hoof and tissue samples may be gathered. It is helpful to collect samples of any unfamiliar plants to show the veterinarian; this will aid in the evaluation of clinical signs.
In cases of severe toxicity, prognosis is poor. Many horses will die within days of the poisoning. If the horse is able to survive the poisoning, treatment will focus on flushing any remaining toxicity from the system. Possible treatments include a diuretic and activated charcoal. Steroid medication may be given. Making the horse comfortable is a priority, so medication to treat stomach symptoms such as nausea may be given. Dexamethasone and prednisolone have been shown to have success with horses if early treatment is obtained. Veterinarians may also recommend an immediate change to a high protein diet.
It is important to understand that a poisoned horse may never return to previous levels of performance; however, the horse may be able to sustain a healthy, happy life with appropriate dietary changes and care.
A horse’s body depends upon a healthy balance of vitamins, minerals proteins and fats. While selenium is required to maintain cell health and ensure thyroid function, too much (or too little) can prove toxic. Your veterinarian will help you establish the right level of selenium for your horse. A high protein diet may be the most effective choice. Be sure to keep the horse away from high amounts of selenium that may occur in water, food and soil.
Having your hay tested for its mineral content is advisable, especially for horses who have experienced an imbalance. If you’re unsure of the best diet for your horse, it is recommended that you ask your veterinarian for a nutritional plan.
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1 found helpful
My horse is fed vetch hay from Victoria for over a year now. I’ve read it has serious health problems for horses. My horse has pellets, oil, minerals and vetch twice a day and looks healthy and shiny. Overall health seen by a vet is good. We’re the articles referring to fresh vetch eaten from the paddock, or is hay toxic as well.
July 23, 2018
Common vetch hay is fine in moderation, however other types including hairy vetch and crown vetch may cause some toxic symptoms. Depending on the literature, common vetch hay should be fed at around 0.5% of body weight. Regards Dr Callum Turner DVM https://csuvth.colostate.edu/poisonous_plants/Plants/Details/106 https://csuvth.colostate.edu/poisonous_plants/Plants/Details/103 http://ovc.uoguelph.ca/externship/blog/Apparently-all-hay-is-not-created-equally%E2%80%A6 www.cyberhorse.net.au/tve/photos/070607prydes/EasiFibreBrochure.pdf
July 24, 2018
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