In this section we have gathered advice from different experts to provide you with a step by step guide, from your horse’s first blood test through to developing a personalised management plan for your horse.
There are three diagnostic tests that it is helpful to understand when your horse is being investigated for the possible presence of Equine Cushing's disease. The basal ACTH test, the TRH stimulation test, and insulin tests.
We have summarised what these tests are and what they can tell you below.
1. The basal ACTH test
Firstly, what is a basal ACTH test?
There is no perfect test to detect whether a horse or pony has Equine Cushing’s disease, but the basal ACTH test is the recommended first line test for this disease.
Horses with Equine Cushing’s disease produce increased amounts of a hormone called ACTH. By comparing the levels of ACTH in your horse’s bloodstream to the level that is considered normal in horses and ponies in the UK at that time of year, your vet will be able to ascertain whether your horse has Equine Cushing’s disease.
The ACTH levels in healthy horses will fluctuate with the seasons: ACTH levels are naturally higher in the Autumn months of August, September, and October. Autumn is the best time to test for Equine Cushing’s disease because horses with this condition have an exaggerated seasonal variation in their ACTH levels at this time, resulting in exceptionally high ACTH levels compared to healthy horses.
Your vet will also assess the impact that other factors such as severe stress, severe pain and recent strenuous exercise could be having on your horse’s ACTH levels.
It will normally take a few days for the test result to come back from the laboratory, and your vet will then be able to tell you whether your horse’s result is positive, negative or borderline (grey zone).
A positive basal ACTH test result
A positive basal ACTH test indicates that your horse has Equine Cushing’s disease.
Positive results are ACTH values that are above what is considered normal for a healthy horse at the time of year that your horse was tested. In the graph below all values above the pink line would be considered positive results.
Positive results can be close to the pink line, or can be up to 300pg/ml in unusual cases! The actual numerical value is useful to know in order to monitor how effective treatment is, but it is not relevant in assessing how advanced the disease is at the time of diagnosis and does not impact on the likely outlook for your horse.
If you would like to learn more about what to expect after a diagnosis of Equine Cushing’s disease please read ‘Prognosis for Equine Cushing’s disease’
A borderline/grey zone basal ACTH test result
A borderline or grey zone ACTH result is more challenging to understand. Your vet will consider many factors such as the age and breed of your horse, the number and severity of clinical signs, the results of other tests such as dynamic insulin tests, and the time of year when interpreting these results for you.
Borderline results are ACTH values that fall between a positive and a negative result. In the graph below all values between the pink line and the white line would be considered borderline results.
Your vet may interpret a grey zone result as a likely positive; in these cases they may recommend monitoring your horse’s response to treatment, or they may suggest further testing to confirm their suspicions.
Your vet may interpret a grey zone result as a likely negative; in these cases they may recommend investigating an alternative cause for your horse’s clinical signs, or advise monitoring the clinical signs.
In many cases grey zone results are just that; in the grey zone between a positive and a negative result with no clear indication of whether your horse does or doesn’t have Equine Cushing’s disease. In these cases your vet is likely to recommend further tests to investigate whether this disease, or an alternative cause of the clinical signs, is present or not.
A negative basal ACTH test result
A negative ACTH result indicates that your horse is unlikely to have Equine Cushing’s disease at the time of testing.
Negative results are ACTH values that are below what is considered normal for a healthy horse at the time of year that your horse was tested. In the graph below all values below the white line would be considered negative results.
Negative results can be close to the white line, or can be as low as 10pg/ml. The actual numerical value is useful to know in order to monitor your horse. Equine Cushing’s disease is a progressive disease, so if your horse has a negative basal ACTH result but is showing early signs of the disease now it is possible that a repeat basal ACTH test at a later date may indicate a different result.
For this reason it is advisable to monitor your horse closely after a negative basal ACTH result. If the original clinical sign does not improve or if your horse develops other clinical signs of Equine Cushing’s disease you may wish to repeat the basal ACTH test.
You can use the PPID assessment checklist to monitor your horse for signs of Equine Cushing’s disease.
Finally, why are monitoring ACTH tests important and what do they tell us?
It is recommended that a monitoring test is carried out to check your horse’s ACTH levels 4-6 weeks after initiation of treatment, or after any dose change. Once it has been demonstrated that your horse’s clinical signs are well controlled and the ACTH levels have normalised, it is advised that a monitoring test is carried out every 6 months to check your horse’s ACTH levels remain under control.
Please ask your veterinary surgeon for more information about this nationwide scheme.
*free basal ACTH laboratory fees only. Veterinary practices may apply visit, blood sampling and interpretation fees. Only available to horses treated with a specific POM-V medication.
2. The TRH stimulation test
What is a TRH stimulation test?
TRH stands for Thyrotropin Releasing Hormone: this hormone stimulates the pituitary gland to produce ACTH.
The TRH stimulation test is another test which can detect whether a horse or pony has Equine Cushing’s disease. This test takes a little longer to carry out, and is most commonly used as a second-line test in the event of a borderline (grey-zone) basal ACTH test result. Occasionally this test is used as a first-line test in horses and ponies showing very early signs of Equine Cushing’s disease.
When carrying out this test your vet will take a baseline blood sample from your horse before administering an injection of TRH. They will then take a second blood sample after 10 minutes and/or 30 minutes. All blood samples will be sent to the laboratory for analysis. Horses with Equine Cushing’s disease will have a greater increase in their ACTH levels after TRH stimulation than horses without the disease.
Your vet will compare your horse’s result to a reference range in order to determine whether your horse has a positive, negative or grey zone result for the presence of Equine Cushing’s disease. It is recommended not to feed a grain meal to your horse before this test, your vet will advise. This test is not recommended between July and November.
3. Insulin tests
How and why is insulin measured?
Measurement of insulin levels is carried out in order to assess whether a horse or pony has Insulin Resistance (IR). IR is a condition which reduces a horse’s sensitivity to insulin. Animals with this condition will produce more insulin to try to compensate for the reduced sensitivity. As a result, horses and ponies with IR can have higher than normal levels of insulin in their bloodstream, and they can also have an exaggerated response to ingesting sugar, which normally causes insulin levels to peak after eating food containing sugar. This is a problem because high levels of insulin can cause laminitis.
Approximately one third of horses and ponies with Equine Cushing’s disease are thought to have Insulin Resistance. Vets will frequently check for IR in horses that they suspect may have Equine Cushing’s disease because it is so common, and because the presence of IR significantly increases the risk of laminitis.
There are several different ways to test insulin levels in horses. The simplest and most common method is for your vet to take a resting blood sample, ideally 2 hours after your horse has been fed, which is then sent to the laboratory for analysis. This is a useful and simple test to carry out, but needs to be interpreted alongside information about what your horse has recently eaten. A normal resting insulin level does not rule out the presence of IR, although it makes it less likely.
An oral glucose challenge/Karo light syrup test is a more reliable assessment of whether IR is present as this assesses the horse’s insulin response to sugar, however this is a more complex test to carry out. Your horse will need to be fasted overnight then fed a test meal of sugar. Your vet will take blood samples before and after the sugar meal, and then interpret the results to determine whether IR is present.
The outlook for horses and ponies with Equine Cushing’s disease
Equine Cushing’s disease is a common diagnosis for older horses and ponies: It is estimated that one fifth of horses over the age of 15 have this condition so you and your horse are not alone!
There have been huge advances in our understanding of this condition over the last ten years, and although Equine Cushing’s disease cannot be cured, we now know a lot about how to manage the condition so that your horse can lead a happy life. The majority of affected horses respond well to treatment and many of those will return to their previous use, including performance horses.
The cornerstone of effective disease management is a daily medication licensed to treat the signs of Equine Cushing’s disease. Please read ‘Treatment for Equine Cushing’s disease’ to find out more about this.
In addition to medical treatment, there are some important management strategies that can help to ensure a good quality of life for your horse. We have many tips on diet, exercise, and general management to support you in deciding an appropriate plan for your horse. You can read more about these here.
If you can manage the signs of Equine Cushing’s disease with appropriate treatment and management strategies, your horse should be able to live a comfortable and happy life.
Horses with untreated or uncontrolled Equine Cushing’s disease are at a high risk of developing signs associated with this disease such as laminitis, repeated infections, muscle wastage, lethargy, poor coat quality, and increased drinking and urination.
Medical treatment for Equine Cushing’s disease
Medical treatment is the cornerstone of managing your horse's Equine Cushing's disease. This medication is a once-daily tablet to be taken for the rest of your horse’s life.
Once your horse has started treatment, an improvement in the signs of disease is expected within 6-12 weeks (although it is worth noting that it can take longer than this for some signs to improve).
Treatment is lifelong, and your horse will need regular 6-monthly check-ups with your vet so that they can monitor for recurrence of clinical signs and take blood samples to monitor the levels of ACTH in your horse’s bloodstream.
For information on medical treatment click here
General management of Equine Cushing's disease
In addition to medical treatment for Equine Cushing’s disease, it is important to treat some of the clinical signs of this disease. Your vet will be able to advise on appropriate treatment for laminitis or repeated infections, and many horses benefit from the strategies outlined below:
1. Horses affected by abnormal sweating:
Horses and ponies with Equine Cushing’s disease may sweat excessively, either all over or in patches. Regular clipping to maintain a healthy coat, together with rugging as necessary, can help your horse cope with changeable weather conditions and temperatures. It is also important to ensure that your horse has access to adequate shelter when turned out. Although some animals may sweat because of a long or thick hair coat, it’s worth noting that others may continue to sweat excessively even after clipping or in a cool environment
2. Horses affected with an abnormal hair coat:
Those affected by a particularly thick hair coat often benefit from being clipped, particularly during the summer months, however regular clipping of excessive hair coat may be needed throughout the year. In addition to helping them feel more comfortable during warmer weather, clipping can also help to maintain good skin health and help to spot any early signs of skin problems.
3. Horses affected with recurrent infections
Horses and ponies with Equine Cushing’s disease may be more prone to conjunctivitis. Good fly control during the summer months is always important, but for those with Cushing’s disease may also help to reduce the risk of developing an eye infection. Early identification of any secondary infections will also improve the chance of successful treatment, as even minor infections can become difficult to manage in horses with Cushing’s disease.
There are also several management and preventative healthcare measures that are important aspects of keeping Equine Cushing’s disease patients in the best possible health, whether or not they are receiving any medication.
1. Feeding a horse with Equine Cushing’s disease
The correct nutritional support can help your horse or pony cope better with the consequences of Equine Cushing’s disease. Understanding which aspects of the disease can be supported nutritionally, and how to manage the diet so that it doesn’t make the problem worse will help you put together a suitable nutrition plan.
For most horses and ponies with Cushing’s disease, the nutritional requirements are very similar to older animals in general. However, some horses with the disease have clinical signs such as weight loss, obesity and/or a predisposition to laminitis. In these horses it is crucial to feed an appropriate diet to normalise body weight and reduce the risk of laminitis occurring.
Both overweight and laminitis-prone horses with Cushing’s disease will have a high risk of an abnormal insulin response to sugar and starches in the diet. This abnormal insulin response can increase the risk of further episodes of laminitis. To keep the insulin response low (and reduce the risk of triggering laminitis), it is very important that the amount of sugar and starch consumed is low. In general, that means overweight and laminitis-prone horses with Cushing’s disease should be fed a low calorie, high fibre diet, which means mostly forage. It is important to remember however that the forage can be deficient in protein and micronutrients, so you will need to feed a high quality balancer.
Underweight horses with Cushing’s disease require enhanced nutritional support to enable them to return to normal condition. They can also have abnormal insulin responses and so their diet also needs to be carefully managed to ensure any risk of laminitis is minimised.
For more detailed information please read our advice sheet, written by Teresa Hollands BSc(Hons), MSc(Nutrition), PhD R.Nutr Senior Teaching Fellow in Veterinary Nutrition at the University of Surrey and the nutrition section of our Owner’s Information Guide.
2. Exercising a horse with Equine Cushing's disease
There is no reason to stop exercising a horse diagnosed with Equine Cushing’s disease, however It is important to take veterinary advice when exercising horses with a history of, or active laminitis.
Horses with Cushing’s disease not suffering from laminitis can continue to be hacked and schooled at the same level as they were before their diagnosis.
Exercise can play an important role in the management of Equine Cushing’s disease and Equine Metabolic Syndrome (EMS), and in controlling obesity. If you think it would be appropriate to increase your horse’s exercise levels it is advised to discuss this with your veterinary surgeon, and make gradual small changes to their regime rather than any sudden increases in work.
3. Dental Care
Equine Cushing’s disease does not directly increase the likelihood of dental disease, however it is thought that increased susceptibility to infection results in gingivitis (inflammation of the gums) and periodontal disease often being diagnosed in horses with the condition.
As dental problems are so common in horses with Cushing’s disease, and they may exacerbate other signs associated with this disease such as weight loss; regular and thorough dental examinations (every six months) by your veterinary surgeon or a qualified Equine Dental Technician (BAEDT) are recommended.
4. Hoof Care
Horses and ponies with Equine Cushing’s disease are at a higher risk of laminitis. The hoof changes associated with laminitis can be picked up earlier and managed more effectively if horses with this disease are examined regularly by a farrier.
In addition to this, horses and ponies diagnosed with Cushing’s disease are usually older, and hoof problems are more common in all older horses and ponies. Studies also show that with increasing age horses are less likely to be shod, and the frequency with which they receive farrier attention is reduced.
However farriers can play an essential role in the early detection of hoof problems, including laminitis. Correct trimming and shoeing can also help in the management of arthritis and other musculoskeletal disorders. Even in unshod animals, a check from a registered farrier every two months is recommended.
5. Vaccinations
Horses with Equine Cushing’s disease can have reduced immunity, leaving them more vulnerable to infections. This makes vaccination even more important.
Just like older humans, even healthy older horses have a less efficient immune system, therefore regular vaccination is very important to protect them against disease, even if they are not regularly travelling or mixing with other horses. Unfortunately, when it comes to tetanus and equine influenza, a higher percentage of aged horses are unvaccinated compared to young horses, and the frequency of vaccination tends to reduce with increasing age. Unvaccinated horses can also compromise herd immunity, as they play an important role in disease transmission during equine influenza outbreaks.
6. Parasite control
As they get older, horses are more likely to carry higher worm burdens, especially if they have Equine Cushing’s disease.
Following wormer administration, worm burdens increase again more rapidly in horses with Cushing’s disease compared with other older horses. This is thought to reflect the reduction in immune function that can accompanies this condition.
A targeted worming programme (incorporating both faecal worm egg counts and a blood test for tapeworm) is recommended when planning a worming strategy for older animals, including those with Cushing’s disease. It is advisable to discuss your worming programme with your veterinary surgeon who will be able to devise a tailor-made plan for your horse.
7. Body Condition Scoring
Body condition scoring (BCS) is a way of carrying out a consistent assessment of the fat cover on your horse or pony. It can be useful both in monitoring your horse’s response to a diet designed to increase or decrease their body condition, as well as a means of monitoring your horse over the long term in order to detect when a dietary change is needed.
A BCS of 5 indicates a high fat cover, and a BCS of 1 indicates a low fat cover. Ideally all horses and ponies should have an average BCS of 3, allowing for it to increase to 3.5 over the summer months when pasture is lush, and decrease to 2.5 over the winter months when less quality forage (grass) is available. This seasonal fluctuation in body fat over the year is an important protective natural mechanism which originated before horses were domesticated, and it is useful to try to reproduce it by managing their diet accordingly.
If you would like to learn how to body condition score your horse you can watch this video by Dr Teresa Hollands.
8. Weight management
The simplest way to measure and monitor your horse’s weight is by using a weigh tape. These are available from most tack shops or online.
It’s important to weigh your horse regularly and keep a record in a safe place. Monthly is ideal for horses with Equine Cushing’s disease so that you can monitor and adapt their diet accordingly.
Lifelong monitoring
Equine Cushing’s disease is a progressive condition that will continue even when horses and ponies are treated appropriately. For this reason it is important to monitor your horse and to regularly discuss ongoing treatment with your veterinary surgeon in order to minimise the risk of recurrence of clinical signs such as laminitis.
Disease progression is monitored using a combination of clinical observations (i.e. how well the clinical signs of disease are controlled) and blood testing (i.e. how well the levels of the hormone ACTH are controlled).
Monitoring ACTH levels
Once treatment for Equine Cushing’s disease has been initiated, it is recommended that your horse’s ACTH levels are re-tested 4-6 weeks later in order to assess the response to treatment.
In most cases the ACTH level will have successfully reduced to below the reference range for that time of year. In these cases the patients are usually maintained on the same dose.
In some cases the ACTH level may not have reduced enough and is still above the reference range for that time of year. These cases are likely to require an adjustment to the dose, with further testing every 4-6 weeks until the horse is stable.
Once a horse is stable on treatment, twice yearly blood samples are recommended to monitor the ACTH levels and ensure that the horse remains on the correct treatment dose.
Care About Cushing's works with our partner veterinary practices to provide free* annual monitoring tests for horses being treated for Equine Cushing's disease. Please ask your veterinary surgeon for further information about this nationwide scheme.
Monitoring clinical signs
After treatment for Equine Cushing’s disease has been initiated, it is recommended that horses and ponies are carefully monitored for the occurrence of clinical signs associated with this condition.
These signs include: laminitis, lethargy, sweating, delayed coat shedding, long curly coat, unusual fat deposits, repeated infections, muscle loss, parasitism, increased drinking and urinating.
You can use our Equine Cushing’s disease assessment checklist to monitor your horse whilst they are on treatment.
It is also advisable to regularly record your horse’s weight and body condition.
*free basal ACTH laboratory fees only. Veterinary practices may apply visit, blood sampling and interpretation fees. Only available for horses treated with a specific POM-V medication.
The treatment for Equine Cushing’s disease is a prescription-only medicine, known as a POM-V, and can only be prescribed by your vet. This section of the website is provided as an information service for owners of horses who have been prescribed the POM-V medicine, Prascend® 1 mg tablets for horses, by their vet. Please click 'OK, I accept' to confirm that you are either a veterinary surgeon or an owner of a horse that has been prescribed Prascend by your vet.
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