Stall-Side Testing for PPID in Progress

Current estimates suggest that pituitary pars intermedia dysfunction (PPID, equine Cushing’s disease) occurs far more frequently than once thought. Now, experts believe that up to 30% of horses over 14 years of age are affected. With this in mind, early testing for horses with clinical signs consistent with PPID is recommended by the Equine Endocrinology Group at Tufts University, and the key test for diagnosing PPID is measuring ACTH blood levels.

Presently, in cases of suspected PPID, blood samples are submitted to a local commercial laboratory for ACTH testing, yet several drawbacks with this protocol exist.

“Pre-analytical variables can negatively influence the blood samples, potentially affecting the test results. For example, inappropriate storage conditions (e.g., excessive heat) after being collected on a farm until reaching the lab and excessive time from sample collection until analysis may alter results, potentially producing false negative or false positive results,” explained Catherine Whitehouse, M.S., a Kentucky Equine Research nutrition advisor.

Thus, having a rapid, sensitive, and cost-effective stall-side test kit that can measure ACTH would be embraced by the equine community.

Taking a step towards achieving this goal, University of Tennessee researchers developed an ACTH test that could turn into a point-of-care or stall-side test.^*

In brief, they identified a “capture” antibody that binds to ACTH in solution (e.g., blood, plasma, serum) and a “detection” antibody used in what is called a sandwich ELISA. As this was only a preliminary, proof of concept study, no further evaluation was performed (e.g., on samples from healthy horses or those with PPID). But the researchers stated, “Further studies are ongoing to optimize and validate our assay using equine plasma and serum samples.”

“This type of test will also improve turnaround time and potentially lower testing costs. This means more owners will test their horses, allowing an earlier diagnosis and avoiding treatment delays,” Whitehouse said.

Early clinical signs of PPID that warrant ACTH testing include regional hypertrichosis (long coat) with or without delayed shedding, loss of topline muscle, lethargy, decreased performance, and abnormal sweating (increased or decreased). Once diagnosed, horses are typically treated with pergolide and followed closely by their veterinarian.

“In addition to medical management, horses with PPID often require dietary modifications to help support weight management, metabolic health, and in some cases targeted nutrition for hoof, skin, and coat health. Consider Kentucky Equine Research’s dual-action hoof and coat supplement, Bio-Bloom PS (Bio-Bloom HF in Australia) if your aged horse is experiencing chronic hoof abscesses or skin and coat issues,” Whitehouse recommended.

^*Neufang, L. J. Ramos, S. Eda, B. Flatland, and L. Giori. 2024. Initial development of a rapid, portable, stall-side ELISA for the measurement of equine adrenocorticotropic hormone. Journal of Veterinary Diagnostic Investigation:10406387241285453.