Pergolide is widely prescribed to treat Cushing’s Disease in horses. However – it can have side effects, and some are very worrying to owners. In this blog, we look at one…

What is Cushing’s Disease?

Cushing’s disease, or Pituitary pars intermedia dysfunction (PPID), is a condition that affects the chemical pathways in the brain. In a normal, healthy horse, hormones are released by the pituitary gland under direction of dopamine which is produced by the hypothalamus. However, in a horse with PPID, there is a change in the amount of dopamine produced by the hypothalamus. This means that the pituitary gland becomes out of control and produces too much hormone. ACTH, the hormone that is produced, is responsible for the common clinical signs; such as increased thirst, increased hair growth, reduced hair shedding and increased urination.

What does Pergolide do?

Pergolide is the most common treatment prescribed for PPID. It is known as a dopamine agonist. This means that it imitates the dopamine molecule and is able to bind to the receptors that dopamine would usually work on. The pituitary gland then reduces the amount of ACTH that is produced and the clinical signs of PPID should start to reduce. Unfortunately this effect is not long-lived and treatment is required to be given every day for the rest of the horse’s life. However, the prognosis is generally good as long as regular monitoring is carried out, with dose adjustments made as required.

Why might the horse lose its appetite?

Dopamine is one of the chemicals involved in a complicated feedback system that controls hunger; with low levels of dopamine being associated with the feeling of being hungry and high levels being associated with the feeling of being full. When pergolide is started, the horse will suddenly have more dopamine in the body and will start to have a reduction in the feeling of being hungry and therefore their appetite may reduce.

What can I do about it?

The effect of Pergolide on the appetite is usually short-lived, with the horse’s normal appetite returning within 7-10 days. However, if their appetite doesn’t return once their body has become used to the drug, you should speak to your vet as the dose may need to be changed. 

Not all horses starting Pergolide will experience a reduction in appetite. But it is best to be aware of it so that you can monitor your horse for any signs. It is important not to change the diet when starting the medication. If your horse does show signs of inappetence, you should offer small amounts of food that the horse is familiar with and usually likes.

How else can PPID be managed?

Most horses with PPID are senior and therefore will need extra care. But having PPID can make a horse more prone to laminitis, as well as infections. It is important to check the body condition score of your horse regularly. This is to ensure that they are in good condition and at a stable weight. Routine dental care is also necessary as this can affect your horse’s appetite. Excess hair growth is a common sign of PPID. This can make the horse hotter and sweatier, therefore regular clipping may help. Your horse should have regular treatment from your farrier, not only will they trim the feet, but they will also check for other problems such as foot abscesses and laminitis.

Regular veterinary checks are recommended to ensure that your horse is responding well to the medication and isn’t showing signs of other diseases. Blood samples will also be taken at these times to ensure that the ACTH is at the correct level. Just as in younger horses, vaccinations and worming should be kept up to date, even if the horse is not going off the yard as they can still pick up diseases.

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