A pony with Cushing's disease

Understanding Cushing’s disease in horses

A long, curly coat that fails to shed normally is the classical clinical sign of Cushing’s disease in horses. However, it is now thought that many more horses and ponies have Equine Cushing’s Disease – which is now referred to as Pituitary Pars Intermedia Dysfunction (PPID) – to some degree, even if they don’t show the most obvious signs.

All breeds and types may be affected, but ponies appear to be at greatest risk. Cushing’s is usually seen in horses and ponies over the age of 15 years, and cases are often in their 20s or 30s. Mares and geldings are equally affected.

The signs of Cushing’s are often vague and variable, and may easily be confused with other diseases or simply put down to “old age”. Weight loss and lethargy are commonly observed, despite a normal or occasionally increased appetite. Loss of muscle mass, particularly over the saddle area and rump, is caused by protein breakdown.

Some horses and ponies may develop the appearance of a “pot belly” due to weakening and stretching of the abdominal muscles. Fat may be deposited along the crest of the neck, above the tail and above and behind the eyes. Sweating is a common sign, particularly in areas where the coat is long. Affected horses may drink and urinate more than usual, although this can be very hard to assess, especially in field-kept animals.

A pony with Cushing's disease

Affected horses may appear more docile and tolerant of pain than others. Recurrent infections (especially dental and respiratory) are common due to suppression of the immune system. In addition, wound healing may be delayed and simple things such as mouth ulcers can become a major problem. Sometimes, there are other potential clues, like the coat that looks as if it has been permed or otherwise inexplicable bouts of laminitis.

Sometimes the link is not recognised, but laminitis is probably the most serious complication of Cushing’s and may be difficult to treat, along with associated foot abscesses. If your horse or pony keeps suffering from pus in the foot, it might be worth checking to see if there is an underlying cause.

Cushing’s (PPID) is caused by progressive nerve degeneration in an area of the brain called the hypothalamus, leading to a reduction in a neurotrasmitter substance called dopamine. Dopamine is important in controlling the secretions of a part of the pituitary gland called the pars intermedia, which in turn is responsible for controlling the secretion of hormones including ACTH and cortisol.

When the pars intermedia is not exposed to enough dopamine from the hypothalamus, the ultimate outcome is the production of abnormally high levels of these hormones, resulting in the symptoms or clinical signs associated with the disease. For this reason, Equine Cushing’s Disease is nowadays termed Equine Pituitary Pars Intermedia Dysfunction (PPID).

Cushing’s can be confirmed via a blood test. There have been periods when the test is free to horse owners in the UK and Republic of Ireland so speak to your vet to see if this offer is running if you’re planning to have your horse tested. Historically diagnosis was made based on the history of the equine and the delayed shedding of a long, uneven coat, as well as other clinical signs.

Cushing’s cannot be cured, but effective treatment can improve the horse or pony’s quality of life.

Management of Cushing’s Disease in horses

The most effective way to control the symptoms of Cushing’s (PPID) is with medication. In addition, supportive management such as clipping, dentistry and weight control will help ensure you’re providing the best quality of life possible for your horse.

Horses with thick coats will sweat, becoming uncomfortable and distressed in warm weather. They will benefit from regular clipping, particularly in the summer.

Dental care is very important to help prevent infections and maximise the absorption of nutrients from the diet. Dental problems can lead to painful chewing and quidding will reduce appetite and further exacerbate weight loss.

Careful assessment of diet is necessary and giving a pelleted feed designed for older or veteran horses may be helpful. At the same time it is important to minimise the risk of laminitis: professional advice from a nutritionist may be needed to ensure a balanced diet.

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Nutritional support

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Regular use of a weigh tape is useful to monitor weight, and the diet should be altered accordingly.

Routine foot care is important to help prevent recurrent abscesses and laminitis.

Due to suppression of the immune system, prompt treatment of infection is recommended.

Vaccinations, regular worming and treatment for ectoparasites (lice, etc) are more important than usual and should be kept up to date.

Although a number of different medicines have been assessed as treatments for Cushing’s (PPID), only one has so far demonstrated sufficient treatment benefit and safety to the medical authorities to become a licensed treatment. This treatment contains pergolide, which acts to replace dopamine.

In a small number of cases, other medications may be prescribed by a vet including:

  • Bromocriptine (replaces dopamine production)
  • Trilostane (inhibits cortisol production)
  • Cyproheptadine (inhibits serotonin production)

An improvement in a horse’s demeanour and attitude may be seen within 1-2 weeks of commencing treatment; however, changes to the hair coat can take up to six months to show a full improvement.

Treatment does not completely halt the progression of the disease, but it can lessen the clinical signs and improve the animal’s quality of life.

Cushing’s Disease in horses cannot be cured and often develops slowly over a period of several years. Treatment may extend or improve the horse’s quality of life, but medication is expensive and once started must be maintained.

Many affected horses and ponies are able to live comfortably with good management for at least a couple of years. But ultimately, recurrent bouts of laminitis or infection are likely to necessitate euthanasia.