Equine Cushing's disease is more correctly known as pituitary pars intermedia dysfunction (PPID). It involves the pituitary gland, which is a gland located at the base of the brain. This gland is normally controlled by a substance called dopamine and its role is to produce a variety of hormones which play an important role in maintaining and controlling a variety of bodily functions. Horses and ponies with Cushing’s don’t produce enough dopamine which means that the pituitary gland becomes uncontrolled, and produces too many hormones. One of these hormones is called ACTH, but it is likely that there are many others.
The disease primarily affects those over the age of 10, with 19 being the average age at diagnosis. Ponies are more likely to be affected than horses, but mares and geldings are equally likely to be affected.
Signs of the disease include:
- Increased coat length, and failure to shed coat in summer
- Weight loss and muscle loss, particularly topline
- Polydipsia and polyuria (increased drinking and urination)
- Increased sweating
- Immunosuppression, meaning affected animals are more susceptible to infections such as sinusitis, skin infections and parasitism, foot abscesses and also slow wound healing
Diagnosis is based on history, clinical signs, and specific hormone tests. Testing for the disease, by blood sample, is complicated by:
- The slow progressive nature of disease
- False negative results are common for all tests early in disease
- Tests are much more reliable as the disease progresses
- Seasonal variation in hormone output
Treatment and management
Fortunately, extremely effective treatment for PPID is available in the form of pergolide (Prascend) and this drug has been licensed specifically for horses. Pergolide stimulates receptors in the brain and thereby replaces the activity of the damaged nerve supply to the pituitary gland. This results in reduction of hormone production to normal levels. The dose range is wide so the improvement in clinical signs and blood ACTH levels is used to determine the best dose rate for each horse. Pergolide is considered a safe drug. The most common side effect is reversible loss of appetite when treatment is started. This often resolves when pergolide is stopped and then re-started at a lower dose, before being increased more gradually until the ACTH level is within the normal range.
We are delighted that we are partnering with Care About Cushings again and you will be eligible to claim your free ACTH monitoring voucher once every 12 months.
If you have any concerns regarding your horse’s health, please call us for advice.