Cushing's Signs. Too much weight, a cresty neck and balls of fat on the rump and neck are among the classic signs of Cushing’s disease.

When it comes to determining the most common cause of laminitis, a recently completed study at the University of Pennsylvania’s School of Veterinary Medicine places equine Cushing’s disease right at the top of the list.

Over a 6-year period at the school’s New Bolton Center, all horses in the primary care veterinary practice of Mark Donaldson that developed laminitis were tested for equine Cushing’s disease. This was done by evaluation of plasma adrenocorticotropin (ACTH) concentrations, which is one of many hormones that are secreted in excess by the dysfunctional pituitary gland. The assistant professor of medicine found 70 percent of the horses with laminitis also had Cushing’s disease as defined by high levels of the ACTH hormone.

Nearly 79 percent of the horses with Cushing’s disease also suffered from chronic laminitis compared to only 42 percent with normal ACTH levels.

The most common cause of laminitis among these horses was pituitary pars intermedia dysfunction, also known as equine Cushing’s disease. With this disease, Donaldson says the pituitary and adrenal glands produce abnormal amounts of hormones that play a vital role in the regulation of metabolism and inflammatory and immune responses.

While Cushing’s is typically considered to be more common in horses over 20 years of age, results from this study indicated that the disease is common in horses in their teens. While progress of the disease can be relatively slow, it sometimes develops more rapidly and is more severe in younger horses. Changes in body condition are also common. The horses in this Pennsylvania laminitis study ranged in age from 3 to 28 years, with a median age of 15.5 years.

Watch For A “Cresty Neck”

With laminitic horses, Donaldson says shoers should be on the lookout for abnormal fat distribution, one of the most common clinical signs. This fat can accumulate in the neck, on top of the back and over the tail head — even in a horse with a visible outline of the ribs.

Donaldson says only one-third of the group of horses had a long hair coat, another conspicuous sign of Cushing’s disease. However, 20 percent of the horses suffering from Cushing’s didn’t have other clinical signs.

Seasonal Worries

In 21 percent of the horses with Cushing’s disease, the onset of laminitis occurred during September. In laminitic horses not suffering from Cushing’s, laminitis was more likely to occur in May.

“Excess consumption of lush grass was commonly blamed for laminitis in many horses that also had equine Cushing’s disease,” says Donaldson. “Dietary modification of horses with Cushing’s disease may be helpful in preventing this serious complication.” Seasonal variation in grass nutrient quality can also lead to laminitis.

Seek Veterinary Diagnosis

If a horse develops laminitis for an unknown reason or because of being overweight, Donaldson says a Cushing’s evaluation should be done by an equine vet.

Previous studies have indicated that the most effective treatment for Cushing’s disease is pergolide, which suppresses secretions of hormones from the abnormal pituitary gland. Besides dietary modifications and corrective shoeing, Donaldson says treatment with pergolide results in an improvement in laminitis with horses suffering from Cushing’s. Since a large dose range exists, the dose must be titrated based on endocrine function tests such as plasma ACTH concentration, he says.

“Be on the lookout for abnormal fat distribution, one of the most common Cushing’s clinical signs...”

For More On Cushing’s vs. laminitis, See:

  • “Hypothyroidism: A Link to Laminitis?” Julie Orchard, American Farriers Journal, Sept./Oct., 1998. Pages 69 to 77.
  • “Insulin Resistance May Be Key To Founder Puzzle,” Pat Tearney, American Farriers Journal, December, 2001, Pages 13 to 21.
  • “5-Step Treatment For Laminitis,” Pat Tearney, American Farriers Journal, Jan./Feb., 2002, Pages 9 to 14.
  • “Laminitis Still A Puzzle?” Pat Tearney, American Farriers Journal, March/April, 2002, Page 107.

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