Tendon Degeneration in Horses with Cushing’s

Classic signs of equine Cushing’s disease, more correctly referred to as pituitary pars intermedia dysfunction or PPID, include:

• Delayed or absent seasonal shedding;
• Exercise intolerance;
• Recurrent laminitis;
• Muscle-wasting and pendulous abdomen;
• Recurrent infections (e.g., sole abscesses, skin infections);
• Abnormal sweating patterns;
• Excessive thirst and urination; and
• Behavioral changes such as dullness or depression.

“These physical changes occur predominantly due to increased levels of circulating cortisol, a potent hormone capable of upsetting many body systems,” explained Laura Petroski, B.V.M.S, a Kentucky Equine Research veterinarian.

In particular, high levels of cortisol may disturb certain musculoskeletal structures of PPID horses, like tendons and ligaments. One research team* recently hypothesized that degeneration of the suspensory ligament frequently observed in older horses with PPID could be secondary to high cortisol levels.

To explore this, researchers collected suspensory ligament samples of horses with or without PPID. Samples were analyzed for the presence of glucocorticoid receptors capable of binding cortisol and the presence of the enzyme responsible for converting inactive cortisone to active cortisol called 11βhydroxysteroid dehydrogenase.

“Researchers found an increase in both glucocorticoid receptors and 11βhydroxysteroid dehydrogenase in the suspensory ligament samples obtained from PPID horses. These findings suggest that altered cortisol metabolism by the suspensory ligament contributes to degeneration of that ligament in horses with PPID,” summarized Petroski.

The researchers suggested assessing the suspensory ligaments of any horse diagnosed with PPID. Corrective trimming and shoeing to address suspensory ligament degeneration, in addition to the chronic laminitis that frequently occurs in affected horses, were recommended.

“Pergolide remains the only FDA-approved medication for horses with PPID; however, nutritional management and exercise, if soundness is not an issue, also help manage these horses,” Petroski added.

Horses with PPID may benefit from the use of omega-3 fatty acids, especially those found in a fish oil supplement, like EO-3. The omega-3 fatty acids DHA and EPA are known to strengthen immune function and improve glucose tolerance.

To support hoof health in PPID horses, look for Bio-Bloom PS (Bio-Bloom HF in Australia), a nutritional supplement produced by Kentucky Equine Research containing key nutrients such as biotin, methionine, iodine, and chelated zinc.

For more detailed information about how best to nourish a horse with PPID, consult with a Kentucky Equine Research nutrition advisor today.

*Hofberger, S.C., F. Gauff, D. Thaller, et al. 2018. Assessment of tissue-specific cortisol activity with regard to degeneration of the suspensory ligaments in horses with pituitary pars intermedia dysfunction. American Journal of Veterinary Research 79(2):199-210.