Equine Cushing’s disease is something we see quite often in our older horses.
About one in five horses over the age of fifteen will develop it, and the likelihood continues to rise with each passing year, reaching nearly a third of our most senior companions. Many horses begin to show signs in their late twenties and thirties.
Ponies and native breeds can be a bit more susceptible, but truly, this is an illness that comes with aging. It’s uncommon in the young, yet some horses may begin showing early signs at 7-10 years, with many receiving a diagnosis around 19-20.
What is Cushing's disease in horses?
This condition is more correctly known as Pituitary pars intermedia dysfunction (PPID) and involves the pituitary gland, situated at the base of the brain, and responsible for hormone production in response to brain signals.
In PPID, normal hormone production is affected, and inhibitory function is lost so there is excessive production of hormones from the pituitary. The hormones enter the circulation and produce a host of symptoms of which increased coat length is just one.
What causes Cushing's?
Cushing’s has traditionally been associated with enlargement of the pituitary gland and a subsequent deregulation of hormone production. Although the pituitary is called the ‘master gland’ because it controls the endocrine system, it is actually the hypothalmus which regulates the release of hormones from the pituitary gland.
The hormone which restrains pituitary secretion is dopamine and when dopamine levels are reduced the pituitary releases high levels of hormones including ACTH and the adrenal gland responds by releasing high levels of cortisol. It’s believed that a combination of the two hormones produces the symptoms associated with Cushing’s.
What are the symptoms of Cushing’s disease?
It is important to understand that all equines are individuals and not all animals will develop a long curly coat, some of the symptoms might be very subtle, so the only way to be sure is to consult your vet and have your horse or pony tested for Cushing’s.
One of our customer's horses with Cushing's disease.
Symptoms include:
- Increased coat length and failure to shed in spring and summer
- Weight loss
- Muscle loss which can result in loss of ‘topline’
- Abnormal fat pads above the eyes, the crest of the neck and at the base of the trail
- Increased drinking and urination (polydipsia and polyuria)
- A pot-bellied appearance
- Lethargy and ‘depression’ – often manifested by a lack of interaction with field companions
- Increased sweating
- Chronic and relapsing laminitis
Affected animals are also more susceptible to recurrent infections such as sinusitis, skin infections and parasites.
How can I find out if my horse has Cushing’s?
You need to consult with your vet who will make a diagnosis based on the horse’s history, clinical signs and using specific hormone tests. The two tests used are a measurement of ACTH concentrations or performing a TRH stimulation test – often called the dexamethasone suppression test.
Diagnosis can be plagued by false negative results, particularly early in the disease and seasonal variation in hormone output. Many vets (and owners) are reluctant to use the dexamethasone suppression test in horses and ponies with a history of laminitis as there is a perception that the dexamethasone can trigger laminitis.
A study at Michigan State University has indicated that this risk is probably smaller than originally thought. The test for elevated levels of ACTH is therefore the first port of call, however it is usually less accurate because levels fluctuate with the time of day and season.
Seasonal influences such as shorter days can result in elevated ACTH levels in normal horses, for this reason most vets avoid using this test between August and November.
The most effective test is to combine the dexamethasone suppression test with a similar analysis using thyrotropin-releasing hormone (TRH). This test is less frequently used as it requires additional sampling and is costly, however researchers at the University of Tennessee have found that it is very accurate.
What management options are there?
Cushing’s cannot be cured, however management of the symptoms can be very effective in many cases. The drug of choice for most veterinary professionals is pergolide mesylate (brand name in the UK is Prascend) which helps to regulate the pituitary gland.
Most Cushingoid animals will remain on the drug for life and there is some concern about resistance building up over time which means an inevitable increase in dosage.
It is worth, following discussion with your veterinary professional, investigating some complementary therapies which can be effective at managing symptoms either before pergolide treatment starts or in conjunction with the drug.
Field trials with the herb Vitex agnus castus which helps support hormonal balance have shown very positive results.
How can I manage the symptoms of Cushing's in my horse?
Supplements - Hilton Herbs offers herbal supplements as alternatives or supportive options for managing symptoms related to Pituitary Pars Intermedia Dysfunction (PPID), also known as Cushing's disease, in horses.
Their natural composition supports your equine companion’s energy levels and helps them feel more comfortable and content throughout seasonal changes.
Ideal for horses needing gentle hormonal support, Cush X offers a reassuring, holistic approach to maintaining balance and wellness inside and out.The primary ingredient in these supplements is Chaste Tree Berry (Vitex Agnus Castus).
Diet – low carb/high fat will help counter muscle loss where present and help reduce the risk of insulin resistance. Limit access to rich pasture.
Parasite control – Cushing’s horses are more susceptible to internal parasites so discuss a deworming programme with a focus on worm counts with your veterinary professional.
Dental care – Cushing’s can increases the risk of dental disease and sinus infections so regular check-ups are recommended.
Farriery – hoof abscesses and laminitis are a frequent risk with PPID horses so regular farriery care is vital.
Grooming – a full body clip can help as shaggy-coated horses can struggle in warm weather.
Ask your veterinary professional to check your horse’s ACTH levels at least once a year to monitor the effectiveness of any management.