(Edited press release)
Cushing's disease (CD) has been identified as the most common cause of laminitis among horses seen at the University of Pennsylvania's New Bolton Center. Dr. Mark Donaldson, an assistant professor of medicine at the university's School of Veterinary Medicine, conducted the study. The results of his work will appear in the April 1 issue of the Journal of the American Veterinary Medical Association.
In CD 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.
All horses that developed laminitis during a six-year period (1996-2002) were tested for CD by evaluation of plasma ACTH concentrations. ACTH is one of many hormones that are secreted in excess by the dysfunctional pituitary gland. Twenty-eight of the 40 horses with laminitis were diagnosed with CD. Although CD is considered a disease of older horses with an average age of 20 years, the study showed that CD is common in horses in their teens. The horses in the study ranged in age from 3 to 28 years, with a median age of 15.5 years.
One of the most common clinical signs seen in the study's horses with CD was abnormal fat distribution, including accumulation of fat in the neck ("cresty neck"), top of the back, and over the tail head, in a horse with visible outlines of the ribs. Only a third of the group had a long hair coat, another conspicuous sign of CD. A fifth of the group with CD did not have any other clinical signs.
In 21% of the horses with CD, onset of laminitis occurred during September. Excess consumption of lush grass was commonly blamed for laminitis in many horses that also had CD. Dietary modification of horses with CD may be helpful in preventing this serious complication.
Several studies have shown that the most effective treatment for CD is pergolide, a medication that suppresses secretions of hormones from the abnormal pituitary gland. In addition to dietary modifications and corrective shoeing, treatment with pergolide results in an improvement in laminitis. A large dose range exists and the dose must be titrated based on endocrine function tests such as plasma ACTH concentration. The drug must be administered under veterinary supervision.