Finding a favourite horse flat out in the field or dead in the stable is a very distressing experience. Equally awful is when a previously healthy horse dies suddenly while being worked or watched. In both situations, the initial shock is frequently overtaken by an urgent need to find out the cause of death.

As well as the emotional issues, there will be important questions that should be asked: is there a risk to any other horses? Is it likely that a post-mortem will be required — especially relevant if the horse is insured — and if so how is this organised?

There is also the nagging worry of foul play; the first thing I am often asked is if the horse has been poisoned. The truth is that poisoning is a long way down the list of potential causes of sudden or unexpected equine death. One analysis of 200 cases of sudden and unexpected death in horses and ponies came up with a positive result for poisoning in only two cases: lead in one and nicotine in the other.

In fact, sudden death in the horse is a rare event, although there is an important distinction to be made between a horse that is “found dead” and a genuine “sudden death”.

A genuine sudden death is when a closely observed and previously healthy horse dies. It can be remarkably difficult to tell why a horse has died in such circumstances, unless there are obvious clues such as scorch marks associated with lightning strike, together with the fact that the horse was found just after a thunderstorm.

Another clue would be a large mouthful of yew clamped in the horse’s jaws, plus evidence that they have actually eaten this toxic plant, which is the commonest form of animal poisoning.

Something to think about in advance is that despite extensive and expensive investigations, which can include a full post-mortem examination (autopsy) and
extra toxicological tests, it may be impossible to fully understand the cause of death.

If you really want to know the reason why a horse has died, then you need to be prepared to have a meticulous and thorough post-mortem performed. A trained veterinary pathologist with the facilities to take samples and look in detail is needed. This may mean sending your horse’s body to a vet school or equine hospital with the knowledge and equipment to pick up tiny clues and perform all the tests that may be needed. Apart from anything else, it takes hours to look inside a whole horse, so this requires a vet with the time, patience and a strong stomach to do a proper job.

In humans, heart attacks are frequently found to be a cause of sudden death. For
many reasons, not least because they do not smoke, drink or have a high-cholesterol diet, horses do not develop heart disease in the same way as people. Unfortunately,
if no other cause of death is found, heart attacks are used as a convenient possibility that cannot be eliminated. If the heart is damaged, for instance by a valve within the pump mechanism tearing, it can be seen clearly. However if the actual heartbeat, which is an electrical impulse, stops, there will be nothing to see.

Currently blood tests at post-mortem rarely tell you as much as one would imagine, but technology is advancing and in the future the more we look, the more we will be able to find out.

Sudden death checklist

  • Are there are any other horses at risk or is this a one-off?
  • When was the horse last seen alive? (so a time scale can be established).
  • Check the environment where the horse was found for any clues; for instance, a horse with colic may thrash about before dying, whereas electrocuted horses usually drop dead without a struggle.
  • Check for potential poisons, such as the unfortunate case of someone tipping yew clippings into a pony’s paddock.
  • Any recent changes in feeding, exercise or other management should be considered.
  • Has the horse recently had any medical treatment? It is an unfortunate fact that some horses will have a lethal allergic-type reaction to a routine treatment.
  • Is it possible that a treatment has been administered incorrectly, either by accident or maliciously.
  • The horse’s recent history should be taken into account. A number of sudden deaths are due to cardiovascular catastrophes such as a tear in the aorta, the main artery coming out of the heart. These ruptures are associated with increased blood pressure during periods of activity or excitement, such as racing or in the stallion during the breeding season.
  • The unlikely option of foul play may need to be considered.
  • Read this veterinary feature in full in Horse & Hound (28 July, ’05)

    Get up to 19 issues FREE
    UK’s No1 weekly for Horses for Sale
    Latest results and reports