Understanding Cushing’s disease


Cushing’s disease is one of the most widespread conditions of old age in horses. While it can afflict much younger horses, the disease is most frequently seen in the over-20s, where more than 10% are affected.


A horse suffering from Cushing’s disease is likely to display classic symptoms including:

  • abnormal hair growth and delayed shedding of coat
  • drinking and urinating more than normal
  • susceptibility to infection, ie worms, sinusitis and tooth infections
  • depression and poor performance
  • weight redistribution, often with a pot-belly and fat bulging around the eyes
  • laminitis, chronic and recurrent
  • diabetes-type problems.


Cushing’s is caused by a loss of a neuro-transmitter – dopamine – in the brain. Dopamine inhibits the function of the pituitary gland. As a result, abnormally high levels of hormones are released from the gland, which enlarges.

In the past, tumours of the pituitary gland were thought to be responsible for the condition, but while tumours can develop,they are not always present.


If the vet suspects Cushing’s, tests over more than one visit are likely to be necessary. Once confirmed, there are several different treatment options, but all involve medication.

The drugs most commonly used to combat Cushing’s are not licensed for horses and are, in fact, human drugs.

Pergolide can be used to increase the activity of dopamine. Other drugs used include cyproheptidine and bromocriptine, and all these drugs must be taken for the rest of the horse’s life.

This means that the cost can be high, although, over time, the dosage can be reduced. The drugs are mixed in with feed or made into a paste which is syringed into the mouth.

Read more about the Royal Veterinary College latest research into Cushing’s disease in Horse & Hound 27 September, 2001 issue.

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Originally published on horseandhound.co.uk