Equine Cushing’s Disease & Metabolic Syndrome
Does your Pony seem to gain weight on air alone? Or do they keep getting bouts of laminitis even when you’ve tried so hard to prevent it? Your pony may be suffering from Cushing’s Disease and/or Equine Metabolic Syndrome. This fact sheet will hopefully help you understand these common but often confusing conditions.
EQUINE CUSHING’S DISEASE
What is Equine Cushing’s Disease?
Equine Cushing’s Disease is a dysfunction of part of the endocrine system (organs that are involved in the release of hormones) called the Pituitary gland. The pituitary gland is located at the base of the brain. A specific area of the pituitary gland is affected called the Pars Intermedia and hence another name for this disease is Pituitary Pars Intermedia Dysfunction or PPID. Enlargement of this region of the gland results in increased levels of hormones being released. One of these hormones is called Adrenocorticotropin hormone or ACTH. ACTH travels through the horses bloodstream to the adrenal glands (near the kidneys) and causes the release of Cortisol. Cortisol is a type of steroid, overproduction of this can explain many of the clinical signs seen with this condition.
Cushings Disease most commonly affects pony breeds however older horses (usually over 15) may also be affected.
What does Equine Cushing’s look like?
Abnormal hair coat and recurrent unexplained bouts of laminitis are the most common clinical signs. The abnormal hair coat can vary from delayed shedding of the winter coat to thick wavy hair growth (upto 10cm) characteristic of this disease, this is called ‘hirsutism’. This occurs as the large pituitary gland impinges on the part of the brain that controls body temperature.
Other less common signs are increased drinking and urination, lethargy, pot belly and possibly recurrent skin/respiratory infections, increased susceptibility to worms and dental disease. You may also notice abnormal deposition of fat, above the horses eye for example where the depression would normally be. You may also notice wasting of the horses skeletal muscles.
Unfortunately the link between Laminitis and Equine Cushing’s Disease is not yet fully understood, it is thought that Cortisol and other similar hormones play a major role in the development of Laminitis, as might a metabolic state called Insulin Resistance.
How is Cushing’s Disease Diagnosed?
Presentation alone may be enough in some cases to make a diagnosis, however in more subtle cases tests to measure ACTH, blood glucose and other hormones may be used.
Treatment & Management of Equine Cushing’s Disease
Currently there is no cure for Equine Cushing’s Disease, thankfully there are a couple of drugs that can help to reduce the effects of the disease and aid management of the affected horse.
Pergolide is probably the most commonly used medication, this comes as a tablet licensed for use in horses called Prascend. Pergolide has been reported to be 80% successful in reducing the severity of Equine Cushing’s Disease.
Trilostane is another drug used for treatment however this does not act directly on the pituitary gland and therefore is not often used anymore.
Management is just as important as medicating affected horses and you should regularly check for wounds and evidence of infection, ensuring prompt veterinary attention where required. Regulary visits from the farrier, dental checks, routine vaccinations and worm egg counts are also important in ensuring an affect horses health. Simple things like clipping excess hair will go a long way to making a horse more comfortable.
EQUINE METABOLIC SYNDROME
What is Equine Metabolic Syndrome?
Equine Metabolic Syndrome (EMS) is a term vets use to describe horses presenting with obesity and/or large regional fat deposits, insulin resistance and recurrent laminitis.
EMS usually affects young to middle aged horses and native pony type breeds.
A horse with EMS is usually a ‘good doer’ they seem to gain weight on little food intake. Regional fat deposits are commonly seen in the crest of the neck, around the base of the tail and in and around the mammary glands of mares or the sheath of geldings. Fat deposits are not restricted to these areas and may also be seen over the shoulders.
As with Cushing’s Disease the association with EMS anf Laminitis is still not fully understood. It is believed that there is a link between Insulin Resistance and the predisposition for laminitis to occur.
What is Insulin Resistance?
Insulin is a hormone that is produced to regulate the uptake of glucose from the bloodstream following eating allowing it to be stored in cells as an energy source. With Insulin resistance this mechanism does not function properly and the body increases the level of Insulin to attempt to overcome its own insensitivity to Insulin. An elevated Insulin level therefore can be reflective of Insulin resistance occurring.
Excessive calorific intake resulting in obesity is the primary cause of Insulin Resistance in the horses as in people. It is now known that fat not only acts as an energy store but released hormones and inflammatory mediators that decrease the bodys sensitivity to Insulin.
Why are Ponies Suseptable to EMS?
Native breed ponies have evolved to survive in the UK climate, enduring long periods through the winter when the grass growth is very slow if at all. Fat deposits laid down from eating the lush grass through the spring and summer help the ponies survive these challenging times through the winter, as the pony draws on their reserves to provide the calories they require.
Ponies in the UK now have access to much improved pastures to graze on, they are also provided with extra feeding all year round, often in the form of concentrates and haylage!
How do we diagnose EMS?
As with Cushing’s Disease, in some cases history and presentation alone can be stringly suggestive of EMS, however clinical signs can be confused with Cushing’s Disease and therefore it is important to rule out this disease. Currently there is no one definitive test for EMS, however blood tests to show levels of Glucose and Insulin and the ratio they have to each other are very uiseful in the diagnosis of EMS.
Treatment and Management of EMS
Weight Loss – buy a weigh tape!
Management of both of these require a lot of commitment, discipline and perseverance on the owner’s part! Obese horses should be placed on diet consisting of HAY & VITAMIN/MINERAL supplements ONLY with NO access to pasture. The hay will ideally be mature grassy hay with high stem to leaf ratio.
Legume hay such as alfalfa should be avoided as these contain higher energy contents, if these are the only hay available it should be SOAKED for at least 30 minutes ideally 24hours before presenting to the horse (do not let the horse drink the water the hay has been soaked in, as this defeats the whole object of soaking the hay!) If in doubt…it is always better to soak hay than not to soak!
The amount of hay to be fed should be 1.5% of IDEAL body weight NOT CURRENT weight:
So for a 250kg pony that should ideally weigh 200kg give 3kg of Hay. (200×1.5% = 3)
Always weigh the hay.
This amount of food should be continued until the desired weight is achieved. If NO weight loss has occurred (using your weigh tape not your ‘eye’) this may be reduced to 1% of IDEAL body weight vitamin & mineral supplementation should be provided at the 1% level.
NEVER FEED BELOW 1% as this can cause the insulin resistance to become worse and promote other conditions such as hyperlipaemia, a condition in which high levels of fat are found in the blood and possibly liver due to fat being mobilised by the horse in response to the feed level being below 1% of ideal body weight (in essence starvation).
Exercise is the other crucial component in managing EMS. Once laminitic feet are sound the horse/pony should start on a programme of 2-3 sessions a week of moderate exercise lasting 20-30 minutes. Intensity and duration can be increased over time. Exercise not only aids weight loss but increases insulin sensitivity.
Other feeds/supplements that can be useful for EMS & Laminitis:
Dodson and Horrell – Safe and Sound
Happy Hoof, High Fibre Cubes
Vitamin A & Biotin @ 20mg/day
Antioxidants – Lysine & Threonine
Omega 3 fatty acids.
All supplements should be used with care