08/01/2021
THE SEASONAL RISE
In the northern hemisphere, starting in July/August horses experience the seasonal rise of a hormone called ACTH, which signals them to prepare for winter, grow a thicker coat, etc. This is completely normal for them.
Problems can arise, however, when this hormonal rise is exaggerated. Issues with improper ACTH levels can lead to hoof sensitivity, weight loss, topline loss, excessive drinking/peeing, udder swelling in mares and sheath swelling in geldings, changes in behavior, or even laminitis (often seeming to "come out of nowhere"). Horses with exaggerated ACTH levels are considered to have PPID/Cushing's Disease.
Many owners test their horses' ACTH levels in the spring to check for PPID issues. When these levels come back normal, they assume their horse is all set for the rest of the year. There is a problem with this assumption, however. During the spring, ACTH levels are naturally at their lowest, and horses with early PPID can have levels well under control at this time, and then "suddenly" founder in the fall when levels rise.
So what can we do to help prevent possible issues during the seasonal rise?
⭐️If your horse has been diagnosed with PPID in the past, consider checking their baseline ACTH levels in late July/early August to ensure their levels are well under control during the start of the seasonal rise. It is possible your PPID horse might need an adjustment in their medication dose to ensure ACTH levels stay within normal levels during this time, which in turn can lessen the risk of laminitis. PPID horses with "normal" ACTH levels the rest of the year can become laminitic during the seasonal rise if their ACTH isn't kept in check.
⭐️If you have a horse that has NOT been diagnosed with PPID but has had any of the subtle symptoms listed above - especially if you've noticed an increase in hoof sensitivity in the fall - ask your vet about testing their ACTH levels. Liphook in the UK has a handy chart for what the "normal" levels should be, on average, for each week in the seasonal rise. Older schools of thought avoided testing during this time of year as the assumption was that "all horses would have high ACTH in the fall," but now the lab ranges are able to differentiate between what is a normal response to the seasonal rise and what is not. Don't avoid testing for fear of a false positive!
⭐️In the future, consider testing yearly to catch any issues as soon as possible. Dr. Andrew Van Eps at New Bolton, a leading laminitis researcher, suggests testing ACTH levels yearly starting at age 10, with the TRH stim test (a more sensitive test used usually in the spring to catch early cases). The earlier we are able to notice these endocrinopathic issues, the more likely we are to prevent laminitis and permanent hoof damage from catching it too late.
This time of year can be nerve-wracking for owners with PPID horses, but with proper preparation and management, it doesn't have to be! Being aware of the potential issues can help owners to better prepare and keep a watchful eye on their horses.