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Equine Cushing’s Disease and Metabolic Syndrome

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.

What is Equine Cushing's Disease?

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.

Clinical Signs of Cushing's Disease

There are many signs that may be seen in horses with PPID:

  • Hair coat is often heavy, long and curly and doesn’t shed normally in warmer months
  • Excessive sweating (including heat stress in hot humid conditions)
  • Increased thirst and urination
  • Muscle wastage leading to a pot belly appearance
  • Lethargy and poor performance
  • Increased susceptibility to infection (particularly sinusitis, teeth, skin and hoof infections)
  • Bodyweight loss
  • Development of fat pads around the eyes, along crest of the neck, above the tail and in sheath area
  • Abnormal season or infertility in mares
  • Laminitis

Diagnosis of Equine Cushing's Disease

Your veterinarian can make a diagnosis of Cushing's disease via blood sample using one of 3 diagnostic tests:

equine cushing's disease diagnosis tests

Often blood insulin levels are also taken to assess whether the horse has concurrent metabolic syndrome.

Treatment of Equine Cushing's Disease

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:

  1. 1

    Clipping the hair coat especially during warmer weather

  2. 2

    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.

  3. 3

    Ensure access to ad lib fresh clean water. Add electrolytes to the diet to replace those lost by increased sweating.

  4. 4

    Maintain active exercise, of course this will depend on whether the horse is suffering from laminitis.

  5. 5

    Regular hoof care, dental examinations and faecal egg counts for parasite control.

What Is Equine Metabolic Syndrome (EMS)

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.

How Vets Test for Equine Insulin Resistance (IR)

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:

  1. 1

    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.

  2. 2

    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.

Management of Metabolic Syndrome

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.

Diet Control

  • The vast majority of these horses will do very well on a diet that is low in non-structural carbohydrates of soluble sugars and starches. For most, this means feeding a forage diet of late maturity hay.
  • It is generally recommended that the non-structural carbohydrate level in the diet should be less than 10 to 12%.
  • To prevent over-eating and control intake, it is wise to limit free access to pasture by using a grazing muzzle.

Exercise Control

  • Daily exercise will not only assist weight control but it can help regulate and improve tissue insulin sensitivity. Of course, exercise is not possible if the horse is showing signs of laminitis. Care needs to be taken to assess regularly for any signs of laminitis. Pasture turnout, while better than stabling, is not an effective form of exercise on its own.
  • Sound EMS horses require dedicated daily exercise starting at 20 minutes daily and working up to one hour of walking at a minimum.

Key Differences Between ECD and MS

key differences between ECD and MS

About the author

Dr Leigh Davidson BVSc, BApplSc

Director at Your Vet Online

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