Equine Cushing’s Disease and Equine Metabolic Syndrome have similar presentations and sometimes occur together which can often lead to confusion amongst horse owners.
However, a thorough understanding of the horse's history and clinical signs will ultimately lead to appropriate diagnostic testing, treatment and management regimes.
While many still call it ECD, the more correct term is Pars Pituitary Intermedia Dysfunction or PPID. Most commonly seen in horses aged over 15 years, it is estimated that 20% of horses over 20 years of age, and 30% of those over 30 years old have Cushing’s Disease. Essentially, it is a disease of old age.
Cushing’s Disease is a complex disorder where there is a dysfunction of the pituitary gland, which in turn leads to over-secretion of cortisol by the adrenal gland. The signs of Cushing’s Disease can present in horses in a variety of ways.
There are many signs that may be seen in horses with PPID:
Your veterinarian can make a diagnosis of Cushing's disease via blood sample using one of 3 diagnostic tests:
Often blood insulin levels are also taken to assess whether the horse has concurrent metabolic syndrome.
It's important to understand that there is no cure for PPID. That said, treatment can resolve many of the clinical signs seen and ensure your horse lives a long and healthy life.
Pergolide, a dopamine agonist, is the main treatment that vets use to regulate the production of hormones.
Response to treatment is generally very good and often your veterinarian will advise other management strategies to assist with control of clinical signs.
This may include:
Clipping the hair coat especially during warmer weather
Feeding to maintain a body weight condition score of 4-6 (using the scale 1-9). What to feed will depend on whether the horse is also suffering from insulin resistance. Generally speaking, calories should ideally come from forage rather than concentrates, especially if the horse or pony is overweight.
Ensure access to ad lib fresh clean water. Add electrolytes to the diet to replace those lost by increased sweating.
Maintain active exercise, of course this will depend on whether the horse is suffering from laminitis.
Regular hoof care, dental examinations and faecal egg counts for parasite control.
Equine metabolic syndrome (EMS) has been defined as the presentation of traits of obesity, insulin resistance and laminitis or a predisposition to laminitis (Frank and others 2010).
In contrast to Equine Cushing's Disease where the disease is primarily seen in geriatric horses, EMS is often diagnosed in young and middle-aged horses and ponies.
Recurrent laminitis is often the first clue that a horse is suffering from this endocrine disorder.
However, it isn't just an obese horse that can suffer from this syndrome. Horses with normal body weight and recurrent laminitis are candidates too.
Insulin resistance is the key to identifying horses and ponies suffering from EMS. When tested, these horses will show a high level of insulin in a blood sample.
Your veterinarian will need to do a blood test in order to determine the insulin concentration present in blood plasma. Prior to testing it's important to ensure that the horse is not suffering an episode of laminitis and the horse is not stressed. These situations can elevate insulin levels. All horses are fasted for 12 hours prior to sampling.
There are two types of tests that can be performed:
A single blood sample that can assess both insulin and glucose concentration.
This test can be a little unreliable with approximately 30% of horses with EMS actually demonstrating fasting hyperinsulinaemia, or high levels of insulin in the plasma.
An oral Glucose Challenge Test is a more accurate test that measures the insulin levels in response to a horse being given a glucose meal.
The horse is either stomach tubed with a glucose mix or fed chaff mixed with 1g/kg bodyweight glucose or dextrose powder. Blood is collected two hours later for testing.
Levels of insulin over >20 μIU/mL are indicative IR.
In horses diagnosed with IR, it is essential that we manage them appropriately to prevent the development of life-threatening laminitis. The key to successful management is dietary control and regular exercise.
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