Cushing’s Disease in Horses: What You Need to Know

Dr Jessica May, UK lead vet at the video vet service FirstVet, sheds light on what Cushing’s Disease is, how to spot the signs of the Disease, and how to manage the condition. 

What is Cushing’s Disease?

Cushing’s Disease in horses is also known as ‘Pituitary Pars Intermedia Dysfunction (PPID)’. It is a condition that affects the pituitary gland, which is located at the base of the brain and is caused by an overgrowth of the cells and enlargement of the gland.

The pituitary gland is the part of the body that is responsible for producing important hormones in response to signals from the brain. These hormones signal to other glands and then to different organs in the body. In PPID, normal hormone control is therefore disrupted. Firstly, natural inhibition of hormone production within the body is lost and hormones are produced excessively. As a result, the pituitary gland becomes enlarged. Secondly, other parts of the pituitary gland become compressed. In these compressed parts of the gland, hormone production is reduced.

Which horses are most likely to have Cushing’s Disease?

Cushing’s Disease is often found amongst older horses and ponies, particularly those over 10 years of age. The average age at diagnosis is 19, although the disease can also affect younger horses. Mares and geldings are both equally likely to be diagnosed with Cushing’s Disease.

What are the signs of Cushing’s Disease?

Cushing’s Disease is associated with a wide range of health issues so, although a horse with the disease may not develop all of these problems, there are a number of clinical signs to look out for. The most important clinical sign to look out for is laminitis because this causes significant welfare problems. This is a condition where blood flow to the inner layers of the hoof (laminae) is disrupted and the laminae become inflamed and painful. This can occur in all four feet but is most common in the front feet. Getting treatment quickly is the best way to avoid laminitis becoming irreversible, so make sure to look out for any signs of discomfort in your horse, such as leaning backwards and putting their weight on their hind legs.

Other signs to be aware of include: a noticeable increase in coat length (hirsutism); delayed shedding of the winter coat; lethargy; increased sweating; weight loss; excessive drinking (polydipsia) and increased urination (polyuria). Affected animals are also more susceptible to infections such as sinusitis, skin infections and parasitism, making grooming and proper maintenance all the more important for horses with PPID.

What should owners do if they think their horse may have Cushing’s Disease?

There are several ways to determine whether your horse has Cushing’s Disease. Knowing your horse’s symptoms will certainly go some way towards establishing a diagnosis, as well as having a good understanding of their medical history. Specific hormone tests can also be used to determine if a horse has Cushing’s Disease. Currently, the two main tests that are used to identify Cushing’s Disease are the measurement of ACTH hormone concentration, or a TRH stimulation test. The tests can help to determine whether your horse’s hormone production is abnormal. However, seasonal variations in hormone production can complicate the test results, especially early in the course of the disease.

 

What does treatment involve?

Treatment for Cushing’s Disease usually involves the use of compounds to control the production of hormones, or the body’s reaction to them. Dopamine agonists (pergolide (Prascend)) can be used to replace lost inhibition of the pituitary gland by mimicking the effects of dopamine. This treatment is effective in 65-85% of cases. However, if it does not work by itself, serotonin antagonists can be used as well. Serotonin antagonists most likely work by increasing dopamine levels to replace lost inhibition in the pituitary gland.

These treatments can have some side effects. Pergolide can cause diarrhoea, depression, anorexia and colic, so there are pros and cons to consider when thinking about treatment. The severity of symptoms varies from case to case, so, in milder instances, owners may decide not to treat the disease. Regulating your horse’s diet, to ensure they are getting the nutrients they need, whilst avoiding overeating, is also an important part of managing the health issues that can come with Cushing’s Disease. To work out what is best for your horse, it is best to get a vet’s opinion on how to approach your horse’s condition, as an individual case.

For owners that opt not to treat the disease using the above methods, it is important to still manage the clinical signs of cushing’s disease in horses, particularly laminitis, secondary infections and excessive hair growth, as well as to carefully manage the horse’s diet, to prevent these symptoms from worsening.

With thanks to Dr Jessica May at FirstVet

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