Equine Cushing Syndrome

What is Cushing's?

The Equine Cushing's syndrome is the most common metabolic disease in mainly older horses. The hormonal disorder is scientifically called PPID (Pituitary Pars Intermedia Dysfunction), which describes the place of origin of the disease, the pituitary gland (pituitary pars intermedia). However, the term Cushing's is better known to horse owners.

Cushing's disease is a typical age-related disease in horses. Australian and British studies have shown that around 20% of all horses over the age of 15 suffer from this hormonal disorder. This means that one in five horses over the age of 15 suffers from PPID. In all 16- to 29-year-old horses, the distribution rises to 64%, and in horses over thirty years of age it is as high as 95%. In the rarest cases, young horses also suffer from Equine Cushing's syndrome.

If the horse has Cushing's the entire hormonal balance is thrown out of kilter so that the metabolic functions are disturbed. This hormonal disorder ultimately affects behavior, but also external changes. A horse cannot be affected by Cushing's but it can be treated well so that it can continue to lead a comfortable life.

Symptoms: Recognize Cushing's disease in horses

The course of Cushing's disease can vary as much as its severity. PPID brings with it a whole complex of symptoms, with three being the most common: poor shedding accompanied by long, curly coat, muscle wasting with emaciation, and laminitis.

The word Cushing conjures up an image for many of a horse with a long, shaggy coat that will eventually curl. Even though this restricts the horse's thermoregulation, this can be remedied by good coat care and shearing. Worse is the possible secondary disease laminitis, which occurs in about 50% of Cushing's horses - especially if the disease is left untreated. New, scientific findings even claim that in the fall, Cushing's is the cause in up to 70% of laminitis patients, and in general, 70 to 90% of laminitis cases can be traced back to a sugar metabolism that is disturbed as in Cushing's disease.

Treatment of PPID is therefore essential. But especially in the early stages, the metabolic disorder does not make it easy to recognize. This is because it begins with subtle signs that are only reflected in a change in the horse's behavior: The horse is exhausted and completely without effort, and its coat also becomes dull. In old age, it is also difficult to distinguish between Cushing's and normal signs of aging, because muscle loss in the back can apply to both cases.

In addition, the symptom complex creates a distinction from the metabolic disease EMS (Equine Metabolic Syndrome) is also difficult. This is because there is also so-called "pseudo-Cushing's", where horses can show typical Cushing's symptoms, but the disease behind the symptoms shown by the horse is a completely different one. Pre-existing diseases such as Equine Metabolic Syndrome (EMS), Equine Asthma (COB/COPD) or laminitis can also be a cause of such symptoms.

15 other symptoms how you could recognize Cushing's disease in horses:

1. Besides laminitistendency to hoof ulcers, bad horn
2. Insulin resistance (diabetes), favors creeping laminitis
3. Light to heavy sweating with no apparent cause
4. Increased drinking (polydipsia) and urination (polyuria) due to kidney dysfunction
5. Impaired vision up to blindness
6. Muscle atrophy, poor muscling especially in the back
7. Weight loss
8. unnatural fat redistribution (fat deposition above the eye), unhealthy fat pads on neck and croup
9. Penetration 
10. Poor wound healing
11. Infertility
12. Milk production in non-pregnant mares
13. Susceptibility to infection, frequent disease
14. Dullness
15. Decline in performance to lethargy

‍Thecause of equine Cushing's disease

Science has not yet agreed on the exact causes of Equine Cushing's Syndrome; there is only conjecture. However, it is known that a disturbance occurs in the hypothalamus, setting off a chain reaction between the hypothalamus, pituitary gland and adrenal cortex. Together, the hypothalamus and pituitary gland form control centers that regulate hormone balance and thus keep the horse's bodily functions running.

The chain reaction begins in the hypothalamus. The hypothalamus releases the hormone dopamine, which in turn sends a signal to the pituitary gland to limit the release of its messenger ACTH (adrenocorticotropic hormone). In older horses or horses with Cushing's disease, the dopamine-producing cells die more quickly, so less dopamine is released. This eliminates the ground substance that keeps ACTH secretion in check. The pituitary gland gets out of control and produces uninhibited ACTH. As a result, it can grow massively (adenoma) to tumor size.

As a result, the messenger substance ACTH sends signals to the adrenal cortex, which now also releases large amounts of cortisol. Cortisol, which is usually released more in stressful situations, now produces the typical Cushing's symptoms.

The rising cortisol level puts the horse's body on alert and under constant stress. This weakens its immune response, making it more susceptible to infectious diseases and laminitis. This fits in with the symptoms described above, as does the horse's lethargy and listlessness, which can be explained by the lack of dopamine.

It is not clear why the dopamine-releasing cells in the hypothalamus die off more quickly. However, some researchers suspect that it is due to the high level of affluence of horses that are fed a high-sugar diet and are not given much exercise (obesity). Stress due to incorrect husbandry and excessive demands are also among the list of assumptions. Likewise the assumption that prolonged administration of cortisone Cushing's can trigger Cushing's disease.

Diagnosis

Cushing's is a rather insidious disease that first manifests itself subtly in a change in behavior before the visible, physical symptoms appear. Therefore, a suspected diagnosis is first made on the basis of typical clinical changes. If the suspicion of PPID increases, the vet can confirm this by taking a simple blood sample and determining the ACTH level in the blood.

Die ACTH-Ausschüttung und demnach seine Werte schwanken zwischen den Jahreszeiten: Bei einem gesunden Pferd liegt der Normwert von November bis Juli bei < 29 pg/ml, von August bis Oktober bei < 47 pg/ml. Bei Cushing-Pferden hingegen liegen die ACTH-Werte deutlich über dem Normbereich: Bereits bei über 50 pg/ml ist der Wert kritisch zu betrachten. Steigt der ACTH-Pegel im Blut auf über 100 pg/ml an, ist das ein deutliches Zeichen für das Equine Cushing Syndrom.

Veterinarian Dr. Alexandra Diefenbach explains in the following videohow the vet diagnoses PPID/ Equine Equine Cushing's Syndrome and what a further course of treatment might look like.

However, when it comes to diagnosis, the veterinarian faces a few hurdles. This is because in the early stages and in certain seasons, the blood sample is often not sufficient. If the situation is still unclear, a TRH stimulation test can be performed. The drug administered stimulates or inhibits the pituitary gland. ACTH levels are then determined before and after drug administration. Within thirty minutes, one has a result. Some veterinarians and veterinary clinics combine the TRH stimulation test with the more elaborate dexamethasone suppression test.

The best time for the test is August to October inclusive. This is because in the fall the ACTH level in Cushing's horses significantly higher than that of healthy horses.

Treatment of Cushing horses

Equine Cushing's disease cannot be cured, but it can be treated. With the help of lifelong drug treatment, the hormone overproduction can be curbed and secondary diseases such as laminitiscan be prevented. Long-term medication can also prevent the pituitary gland from proliferating and thus squeezing other areas of the brain.

It is important that the horse owner draws up an individual treatment plan together with the vet. As a rule, symptoms are alleviated just a few weeks after starting treatment. Nevertheless, the horse should be slowly accustomed to the medication with increasing dosage in order to rule out possible side effects such as loss of appetite, tiredness or colic.

In Germany, there is only one commercially available drug for the treatment of Cushing's disease. The active ingredient is called pergolide mesilate, but is known under the brand name Prascend. Prascend is administered to the horse once a day. It replaces the messenger substance dopamine, which signals the pituitary gland to reduce the release of ACTH. As a result, the cortisol level is also kept low. Swiss studies have shown that 90% of patients quickly improve with a daily dosage of 0.5 to 1 mg per kg of body weight. Further studies show that the dosage may need to be increased after a certain period of time. For this reason, the attending veterinarian should carry out an annual check-up, preferably in the fall.

In addition to medication, there are other treatment options for horse owners to contribute to the horse's well-being:

• General: Regular hoof treatment, dental check, deworming, vaccination.
• Shear if necessary, especially in summer, to prevent skin diseases and allow better climate regulation.
• In winter, tuck in so that an excessively thick, long coat does not form
• Clean regularly to remove felt spots
• Clean the box thoroughly and litter it thickly, especially if the horse urinates a lot (polyuria).
• Sufficient exercise, adapted to the state of health, to avoid overweight
• Treat small wounds to prevent infections
• Avoid stress so as not to put unnecessary strain on the hormone balance

Forecast

The diagnosis may come as a shock to the horse owner at first, but it does not mean the end of the world. With the right treatment through medication, an adapted diet and sufficient exercise, the horse can continue to live a fit life for many years, even with the hormonal disease. However, treatment is a prerequisite for keeping the symptoms, especially laminitis, under control. Laminitis is probably the worst consequence of Cushing's, which can restrict the horse's quality of life to such an extent that it may even be necessary to put an end to its suffering. A vet should therefore always accompany the treatment of a horse with Cushing's disease.

Feeding Cushing horses

Feeding a horse with Cushing's syndrome can also provide useful support. Since 

As horses with Cushing's disease have an increased need for micronutrients, attention must be paid to highly bioavailable minerals and vitamins in organic compounds. At the same time, it is important to keep a close eye on the amount fed and to adjust it up or down if necessary. With good feeding, one makes an important contribution to an improved quality of life of the Cushing's horse.

Groundbait:

An intact intestinal flora has top priority, as it is responsible for the absorption of all important nutrients. Giving sufficient roughage in the form of hay and forage straw is essential. For old horses with dental problems, soaked hay cobs or other roughage substitutes can be given for soaking.

Feed overweight Cushing's patients reduced starch and sugar:

In Cushing's horses with redistributed and strong fat pads, starch- and sugar-reduced feeding is essential. The excess weight can otherwise promote laminitis and insulin resistance (diabetes). Overweight horses should therefore avoid molasses-based muesli and cereals. Grazing should also be reduced, although exercise is important for the overweight horse. Possibly a muzzle could be the solution here. Hay is best soaked to flush out the carbohydrates. However, soaking also dissolves nutrients, so supplementation is needed.

Feeding lean Cushing's horses with severe muscle atrophy

If old horses lose more muscle mass due to Cushing's and are difficult to feed, attention should be paid to the administration of vitamin E, high-quality protein and linseed oil with omega-3 fatty acids.

To counteract muscle loss, essential amino acids are important as building blocks of the muscles. A high-quality source of protein is, among other things, alfalfa, which can be fed to the lean horse as hay or soaked cobs. This is best supplemented with feed oil for that extra energy. Another energy source suitable for lean horses with Cushing's disease is desugared beet pulp.

Mineral and vitamin supply of Cushing horses

The following applies to all horses with Cushing's syndrome: They have a high demand for (micro-)nutrients and antioxidants to support the metabolic processes that are out of balance. When choosing supplements, therefore, much emphasis should be placed on their high bioavailability and starch and sugar reduction.

The disease puts a lot of stress on the liver and kidney function. Bitter herbs can help the organs in their detoxification. These include nettle, milk thistle, birch leaves, dandelion and black cumin.

The horse's defenses are weakened by the high cortisol level. Vitamin C, for example in the form of fresh, dried or powdered rose hips can help the severely weakened immune system of Cushing's horses.

Monk's pepper and preparations thereof are known to have a positive effect on hormone balance, which is why they can be used as a supplement to drug therapy for Cushing's disease. Discuss this with your treating veterinarian beforehand.

‍FAQ- the most frequently asked questions about Cushing's disease in horses

1. how old do Cushing horses get?

No exact age can be given for the life expectancy of a horse with Cushing 's. Each case differs as much as the symptoms, and the horse's treatment and attitude also have a great influence on its life with Cushing's. In most cases, the first symptoms appear from the age of 15 years. If one gets clarity early on with the help of an ACTH test and starts treatment immediately and permanently, the horse's well-being can be maintained and even increased. There are even horses suffering from PPID that have lived up to 37 years.

‍2How much does a Cushing's or ACTH test cost?

The ACTH test is performed by a veterinarian who wants to be paid for his travel and service, as well as the laboratory test. For the performance alone, one must calculate with about 60 € or more.

If the diagnosis is positive, the drug Prascend must then be administered once a day and permanently. Monthly costs of 60 to 120 € can be expected. If additional treatments are required, for example by a farrier, the monthly costs will be significantly higher.

3. May I ride a Cushing's horse?

With Cushing's the cortisol level, the stress hormone, rises sharply. The cortisol level in Cushing's horses as low as possible, as this would otherwise only exacerbate the symptoms. Nevertheless, the horse should be exercised with consistent intensity and frequency in order to stop the rapid muscle breakdown and the development of severe obesity. However, you should take a closer look at how much you expect your horse to do. Riding should therefore be adapted to the horse's state of health. Extensive warm-up and dry riding phases are essential. Alternatively, you can keep the horse busy with sensible exercises from the ground. If a sport horse develops Cushing's disease, the sporting ambitions must also be adapted.

4. how can I prevent Cushing's?

The exact causes for the death of the dopamine-producing cells in the hypothalamus are still unclear. However, the entire metabolism can be supported with species-appropriate husbandry, little stress and a lot of exercise and thus prevent the possible development of Cushing's disease. When feeding, care should be taken to ensure that the amount of feed is adapted to the age and state of health of the animal, in order to avoid overweight and thus not to put further strain on the metabolism. Although this is no guarantee for a hundred percent prevention, it is nevertheless of utmost importance for keeping every horse healthy.

5. Can I breed with a Cushing's horse?

The Equine Cushing's syndrome can lead to fertility problems in mares, so that if a mare suffers from PPID is highly unlikely to become pregnant anyway. Furthermore, pregnancy means high physical and hormonal stress, which should be avoided at all costs in the case of hormonal disease. For the benefit of the horse horses with Cushing's disease should not be bred. Whether Cushing's disease in horses is hereditary in horses is difficult to say, as researchers disagree on what actually triggers Cushing's disease.

6. is Cushing's fatal for my horse?

Not necessarily, as the disease itself is not fatal. However, if left untreated, it can lead to severe secondary diseases such as laminitis can result. If the coffin bone punctures through the sole of the hoof or the hoof is shod out, this means the end of the horse. Since PPID can be treated very well, there are Cushing's patients have a good chance of living a very good quality of life.