The adrenocorticotropic hormone (ACTH) test is a single blood test used to determine if a horse has PPID (pituitary pars intermedia dysfunction, also known as Cushing’s disease).1 A TRH (thyrotropin-releasing hormone) response test measures ACTH. Injection of TRH causes the pituitary pars intermedia to produce increased ACTH.2 Season and stress can affect the ACTH tests.

Researchers from Middle Tennessee State University and Boehringer Ingelheim teamed up to determine if the stress of trailering a horse could result in a false positive for PPID using ACTH testing. Many owners must trailer a horse to the vet clinic for testing. The researchers from Middle Tennessee State were John C. Haffner, DVM, and Rhonda M. Hoffman, PhD. Their Boehringer Ingelheim co-author was Steve Grubbs, DVM, PhD, DACVIM.

This research was presented at the 5th Global Equine Endocrine Symposium (GEES), sponsored by Boehringer Ingelheim.

ACTH Test Research Results

The researchers used 10 adult PPID-negative horses in the study. Five of the horses were hauled 40 minutes every four weeks starting in February 2020. They were rotated through five trailer positions. Beginning in February 2021, the other five horses underwent the same process.

Each horse had blood collected before loading onto the trailer to establish a pre-transport ACTH concentration.

TRH stimulation tests were performed at 0, 15, 30, 60, and 120 minutes post-trailering. The researchers reported no effect of year or day of sampling.

The researchers said a 40-minute trailer ride resulted in “multiple false-positive PPID diagnoses in horses when using basal ACTH for as long as 30 minutes post-trailering. Except for a single horse, T10ACTH (samples collected 10 minutes after TRH administration) does not appear to be elevated by trailer stress.”

Researchers said veterinarians should wait at least 30 minutes after trailering to test horses for PPID when the basal ACTH test is used.

Editor’s note: You can access the full Proceedings of the 5th GEES Symposium here.

References

  1. Equine Cushing’s Disease: Equine Pituitary Pars Intermedia. AAEP.
  2. Equine Pituitary Pars Intermedia Dysfunction/Cushing’s Testing. Cornell University.

  • Kimberly S. Brown
    Kimberly S. Brown is an award-winning writer and publisher. She is the Editorial Director for My Senior Horse. Brown spent 10 years at Equine Network, parent company of My Senior Horse. Prior to that she worked for three years in equine nutrition after she retired from nearly 30 years working at The Blood-Horse. Brown spent the last 15 years of her time at that organization creating and developing The Horse and TheHorse.com.
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