Autumn Challenges for Cushing's Diagnosis, Management

Autumn's chill does not just mean your horse will grow a longer coat. It can also mean he'll have higher natural levels of the hormone plasma adrenocorticotropin (ACTH), which, in conjunction with other factors, can lead to flare-ups of laminitis. Veterinarians recommend that owners test, monitor, and manage horses with metabolic problems carefully during this time of year, realizing that ACTH levels and their effects can be horse dependent.

Since high levels of ACTH can be indicative of Cushing's Disease, also called pituitary pars intermedia dysfunction, or PPID, veterinarians often use that parameter as a test for the disease. However, the spikes in ACTH occur even in healthy horses from September until January and can cause false positives.

"We generally recommend not testing for Cushing's (for diagnostic purposes) during these months," said Anne Wooldridge, DVM, assistant professor of equine medicine at Auburn University. Instead she recommended that owners of older horses that exhibit any of the classic signs of Cushing's during the fall months work with their veterinarians to determine whether they should test or treat horses until diagnoses can be confirmed. Clinical signs of Cushing's can include excessive hair growth, muscle wasting, and abnormal fat deposition, among other signs.

Horses with Cushing's disease are at particular risk of laminitis, but the condition can develop in normal horses as well. Beth Kennalley of The Founder Rehab Ranch, a rescue organization near Clayton, Calif., that focuses on horses with laminitis and metabolic disorders, avoids feeding hay that could cause a spike in ACTH levels, and she recommends having every batch of hay tested. "We shoot for less than 10% total sugar plus starch--nonstructural carbohydrates," she said. If this is not feasible, soaking hay in cold water for an hour might remove up to one-third of the sugar.

"Older horses and those starting to develop Cushing's typically have higher rises (in hormone levels), which can lead to unexplained episodes of laminitis in the fall," said Eleanor Kellon, VMD, co-owner of the Yahoo Equine Cushing's and Insulin Resistance Group. "This may occur for years before the horse develops the classical coat changes or tests positive at other times of the year. I recommend treating these horses with pergolide (pergolide mesylate, a common drug for treating PPID) at least during this high-risk period. Diet control alone won't be enough."

Read more at "The Science of Seasons Behind Laminitis, PPID."   

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Jennifer Walker

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