A Guide to Poisoning in Horses: Diagnosis, Treatment and Heavy Metal Poisoning

A poison is a compound that irritates, damages body tissue or alters the metabolism. Because horses are trickle feeders and graze for the majority of the time they are awake, on rare occasions they can eat something poisonous. This guide looks at the types of poisoning a horse can suffer from, spotting the signs of poisoning and what to do if you think your horse may have been poisoned.

Some horses may be more at risk than others when it comes to poisoning. Older or younger horses, those suffering from parasitic infections, the malnourished or horses with a damaged liver or kidneys can’t deal with poisons as well as the healthy, mature horse.

This guide has been broken down in to parts and will be available in its complete form as an ebook shortly after the guide is complete.

You are currently reading: Diagnosis, Treatment and Heavy Metal Poisoning

  • Part 2 – The Dangers of Biological Poisons [Read Now]
  • Part 3- A Guide to Poisonous Plants [Read Now – Coming Soon]

Diagnosing a Poisoned Horse

In most cases it is difficult to determine the cause of poisoning in a horse because the majority of toxic substances cause similar symptoms.

Instead of trying to diagnose the horse, it is often easier to take a look around where the horse was stabled or roaming and attempt to spot any possible poisons.

This guide will help you to determine which substances can be poisonous so you can remove them for your horse’s or pony’s environment.

Although the symptoms caused by different types of poisons can be quite similar, the method of treating them can differ, which is why it is important that, where possible, the poisonous substance is identified. If nothing can be found in the field, paddock or stable, then samples of the poisoned horse’s faeces, feed, stomach contents or body tissues may be required. A qualified vet or similar professional will be able to analyse these samples.

Spotting the Signs of Poisoning

Common symptoms of a horse that has been poisoned include (but are not limited to):

  • Loss of appetite
  • Lack of coordination
  • Lameness or gait irregularities
  • Diarrhoea
  • Laboured or irregular breathing
  • Muscle twitching
  • Discoloured urine
  • Excess salivation
  • Excessive thirst
  • Jaundice
  • Blindness
  • Pupil dilation
  • Colic
  • Swelling around the face, eyes or neck

Treating a Poisoned Horse

A poisoned horse, in nearly all, serious cases, is going to require veterinary treatment. If the poison has been ingested (some poisons can enter via the surface of the skin), the vet will attempt to wash out the stomach of the horse in the hope of removing the poison.

There are also certain substances, such as activated charcoal, which can be given to the horse to absorb the poison and prevent the body absorbing it instead. Time is of the essence as the greater the time between ingestion of the poison and treatment, the more of the poison that will be metabolised and absorbed by the body.

If a horse is suffering from heavy metal poisoning, then chemical compounds will have to be given to attempt to reverse the damage caused by the metal.

Laxatives may also be given to speed up the passage of the poison through the body and decrease the amount of poison that is absorbed.

If you think your horse has been poisoned, there are a couple of things you can do:

  • If the poison has entered through the skin, be sure to continually wash the site of entry – Do not use soaps or detergents as this can speed up the rate at which the poison is absorbed
  • Where possible, retain a sample of the toxin so the right treatment can be given when arriving at the vets/when the vet arrives
  • Seek veterinary aid as soon as possible

Types of Poisons

Listed below are the major types of poisons that you may come across during your time as a horse owner. Although occurrences of poisoning aren’t common – it is always good to be prepared and be able to remove potential poisonous substances from your horse’s environment before they become a problem.

Heavy Metals

Heavy metals such as lead, mercury or arsenic can build up in the environment through pollution or human carelessness. In some cases, these metals can even build up naturally in the environment, making some soils and the plants that grow there, more dangerous than others.

Arsenic – A well known poison, known for the damage it can cause to humans too. Arsenic is rarely found naturally in a stable or field environment. Watch for human waste such as car batteries, which can leak this deadly metal (and others) in to the environment. Arsenic poisoning will severely irritate the gut and may cause staggering and paralysis.

Cadmium – Fields near factories, mines or sewage works may be at risk of containing higher levels of cadmium. Plants, particularly daisies, can absorb large amounts of cadmium from contaminated soil. If a horse eats a large amount of cadmium-contaminated plants you may notice decreased appetite, diarrhoea and a lack of coordination.

Fluorine – Excessive intake of fluorine causes fluorosis a disease that can cause discolouration and marking of the teeth and in severe cases, calcification of ligaments. Fluorine can be common in the soil or water of some environments, so if you notice unusual markings on the teeth, it may be worth getting their feed tested to check for high levels of fluorine.

Selenium – Selenium can be found naturally in high concentrations particularly in certain areas of the USA and Ireland. In selenium rich environments, the plants will absorb this metal from the soil, posing a risk to horses that graze there.

A sign of selenium poisoning is the loss of hair surrounding the mane or tail. Lameness, loss of appetite, partial blindness, staggering and paralysis are all indicators of severe selenium poisoning. Interestingly, in severe cases of selenium poisoning, vets have given a very small amount of arsenic as a method of treatment.

Lead – Due to the popularity of lead in the last century in items such as paint (and its continued use in some car batteries and fuels), fields and pastures can sometimes contain these toxic items. If the horse is allowed to graze in contaminated fields, they may inquisitively chew at the peeling lead paint of old buildings or gates, or they may attempt to eat items containing lead that have been disposed of in the field.

Signs of lead poisoning include loss of appetite, muscle stiffness and diarrhoea. If you notice unusual items littering your horse’s environment – be sure to dispose of them safely.

Mercury – Mercury poisoning is rare, ironically due to the fact that it is highly poisonous. Because of its toxicity, it is rarely used in manufacturing – however some less toxic mercury-containing compounds are used occasionally. The most common cause of mercury poisoning in horses is due to the use of one of its lesser toxic compounds being used as a ‘seed dressing’.

If a horse has suspected mercury poisoning rapid treatment is required. Inflammation of the mouth, kidneys and gut are signs of mercury poisoning, along with nervousness, lack or coordination, diarrhoea and a lack of appetite.

Molybdenum and Sulphur – Molybdenum and sulphur have an interesting route of toxicity. They are consumed from plants that have taken the metals from the soil and then cause the formation of ‘thiomolybdates’ in the gut.

These thiomolybdates then bind to dietary copper in the gut, reducing the amount of copper that is absorbed by the body. This leads to copper deficiency. This is more common in other ruminants such as cattle and sheep, so if you are aware of livestock copper deficiencies in the area it may be worth supplementing your horse’s diet with a quality copper supplement.

The Complete Guide to Dealing with Poisoning in Horses

Thank you for reading part one of this guide, over the next few days, the additional sections to this guide will be released – identifying more potential poisons for horses. If you aren’t already, follow PetSci on twitter to be notified when the next instalment is released.

When finished, this guide will be available to download as an ebook in its entirety, which will be available here on PetSci.

Read Part 2 >>

About James Watts

BSc Bioveterinary Science. Editor of PetSci. When I'm not writing, learning, discussing, or reading about animals, you know it's the weekend! Currently developing PetSci HealthTrak, the fast and easy way to monitor your pet's weight and calorie intake. HealthTrak offers a simple way to track your pet's progress, helping them achieve a healthy weight and a long, happy life.

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One comment

  1. I think my horse was poisoned intentionally by a neighbour. She developed a cough,which got worse, she had mucus and food coming down her nose.and she couldn’t swallow. The vet came to her several times, she was on a nebuliser for two months twice a day, and was endoscoped twice. Eventually we glad to have her put to sleep, the vet said she had a tumor, but I still think she was poisoned.
    Do you think Tahoe would have had these symptoms if she had been please.

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