Horses are part of an ever growing industry, with over 600,000 horses in the UK, 1.4 million riders and 5 million people with an active interest in the equine industry*. Most people acquire a horse out of choice, so if you make this decision you should think carefully before going ahead. A horse needs lots of love and care, including regular worming, vaccinations and dental care. Owning a horse is time consuming and can be costly; not only will you will need to consider where you will keep your horse, you must also consider the ongoing costs of owning a horse which include accommodation, bedding, feed and healthcare.

In the unlikely event that your horse goes missing it is going to be very difficult for anyone to know who it belongs to, unless your horse carries some form of permanent identification. It is wise to get your horse microchipped or freezemarked, this will avoid heartache in the long run, should your horse go missing or is stolen.

Horses are herd animals, and thrive on being together with other horses. Don’t forget that your horse will need somewhere to graze, a stable for warmth in the winter time, a constant supply of water, feeding daily and regular exercise. It can cost hundreds of pounds a month to care for a horse, including accommodation, food, veterinary care and insurance; there will be other costs, including buying tack and rugs and extra livery charges when you go on holiday.

Horses can live into their thirties, over this time your horse will need lots of care and attention. Being able to provide all of this will ensure you and your horse make the most of your time together.

* Research conducted in 2004 by the Henley Centre for DEFRA and the British Horse Industry Confederation.

Seasonal pasture myopathy - atypical myopathy

Atypical myopathy is a highly fatal muscle disease of grazing horses. Ingestion of the toxin hypoglycin A, found in sycamore seeds, has been identified as the cause of the disease. Clinical signs can vary from mild lethargy and muscle stiffness to sudden death, with numerous horses on the same grazing potentially affected. Early diagnosis and rapid implementation of supportive treatment is vital, however fatality rates remain high.

What is atypical myopathy?

The disease known as atypical myopathy (AM) in Europe and Seasonal pasture myopathy (SPM) in USA is a devastating muscle disease which was first recognised in grazing horses in 1939. Since then, it has been reported in UK, Europe, USA, Canada, Australia and New Zealand and the incidence appears to be increasing over the past few decades. In North America, only a few horses tend to be affected on a given pasture, whereas in Europe large outbreaks may occur with many horses on the same premises being affected.

It is seen most commonly in the autumn, but can occur year-round, with fewer numbers of affected horses being seen in the spring and summer.

It can affect horses of all ages, breed and sex, although younger horses are more frequently affected, and it is fatal in 75-90% of cases.
In the USA the disease is linked to the Box Elder tree (Acer negundo); whilst in the UK the European Sycamore tree (Acer pseudoplatanus) is thought to be the cause of the majority of cases. The seeds from both trees contain the toxin Hypoglycin A which is capable of disrupting fat metabolism within the skeletal and cardiac muscle fibres. The amount of hypoglycin A in sycamore seeds varies widely, therefore the number of seeds necessary to cause disease also varies widely. Climatic factors may also affect the concentration of hypoglycin A within seeds, contributing to the variable nature of the disease from year to year.

Ingestion of sufficient quantities of either the seeds in autumn or the seed/seedlings in spring results in  a dose of toxin capable of causing damage to the respiratory, postural and cardiac muscles which may result in death. When one horse becomes affected, the herd mates are also at risk. However, not every horse pastured near box elder or sycamore trees will develop the disease. Risk of disease is affected by numerous factors, including the number of trees near a pasture; the number of seeds on a given tree; the amount of hypoglycin A toxin in the seeds; the environmental conditions affecting seed fall from the tree; the degree of negative energy balance in the horse; and the predisposition of horses to eat the seeds. For example, high winds may increase the number of seeds falling onto a pasture and a lack of other supplemental feeds may promote ingestion of seeds, which results in ingestion of a toxic dose of hypoglycin A.

What are the signs of atypical myopathy?

Symptoms include:

  • Dark coloured urine
  • Muscle stiffness/weakness unrelated to exercise
  • Muscle tremors
  • Lethargy and quiet demeanour
  • Some cases show colic-like symptoms
  • Choke-like retching neck spasms
  • Frenzied vocalisation
  • Vigorous head shaking/nodding/low head carriage
  • Sweating, depression and signs of pain
  • Lying down unwilling to stand but eating
  • Rapid shallow breathing
  • Complete collapse
  • Found dead in the field

The initial symptoms can progress rapidly with many cases developing difficulties in eating, breathing, heart problems and unable to stand up before death within 24-72 hours of the onset of the clinical signs. The signs can be confused with colic, acute laminitis and other muscle diseases such as exertional rhabdomyolysis; veterinary attention should be sought immediately when horses grazing pasture present with signs of being unwell, particularly in the autumn.

How is atypical myopathy diagnosed?

A diagnosis of atypical myopathy is made based on the presence of box elder or sycamore seeds or seedlings on the pasture being grazed, other horses grazing the same pasture being affected, time of year, clinical signs, discoloured urine and blood tests revealing very high concentrations of the enzymes suggestive of muscle damage (creatine kinase and aspartate aminotransferase). If necessary, biopsies of the muscles can be examined under the microscope. Measurement of hypoglycin A and acylcarnitine concentrations can also be performed at specialist laboratories.

Can my horse be treated?

Early referral to a suitable hospital is vital, particularly whilst the horse is still able to stand and be transported. Horses often deteriorate over the first 48-72 hours and require intensive nursing and supportive care.
Treatment is supportive and includes intensive intravenous fluids, which may be supplemented with glucose, anti-inflammatories, painkillers, multivitamins and vitamin E. Treatment is generally more successful when affected animals are identified in the early stages of disease, but high fatality rates exist despite intensive therapy, and treatment can be very expensive.

What is the prognosis for my horse?

The prognosis is often poor; the disease is fatal in 75-90% of cases.
Positive indicators for survival include normal mucous membrane (gums) colour, normal body temperature, remaining standing and able to pass droppings. Indicators that survival is less likely include not eating, difficulty breathing, high heart rate and lying down for prolonged periods.
There is a better prognosis if an affected horse survives the first 4-5 days. Surviving horses can return to their previous level of health and athletic ability.

How can I prevent my horse from contracting atypical myopathy?

In order to prevent your horse from contracting atypical myopathy, it is essential to prevent ingestion of the box elder or sycamore seeds and to ensure that there is sufficient alternative food available. Therefore, the following are recommended:

  • Section off areas around box elder or sycamore trees and collect and dispose of seeds or seedlings safely away from horses
  • Regularly inspect fields to ensure seeds have not blown in from sycamore trees nearby
  • Remove young sapling plants
  • Limit turnout; ideally stabling horses overnight between October and December
  • Supply extra hay or haylage in field when the pasture is poor
  • Reduce stocking density, so there is enough grazing for every horse
  • Ensure access to fresh drinking water. Fence off any ponds/streams under sycamore trees as the toxin is water soluble
  • Allow access to a mineral/vitamin supplement
  • Ensure you check your horse regularly at least twice daily
  • Be vigilant of the potential signs of this disease and contact your veterinary surgeon immediately if your horse becomes ill
  • If a case of atypical myopathy occurs, remove all horses from the affected pasture, check muscle enzymes, supplement with vitamins and minerals, and give a fat-free diet