You’ve heard it before. ACTH rises in the fall. How does that impact our horses? And how can you best care for your horse?
◆︎ Why the seasonal changes?
Horses have a complex hormonal response to the change in seasons. Some events that cause seasonal hormonal changes:
Reproduction: Gestation is about 11 months in the mare. This is important because if the mare is bred in February (northern hemisphere) and foals the following January, the foal could easily freeze to death. The mare would also be so compromised that she could die also. Many mares turn off their reproductive system in the fall.
Interestingly, stallions also have a change of hormones in the fall. It is at this time that they slow down the reproductive hormones. It is theorized that this is to conserve body condition through the winter. Geldings, despite their status, have hormones (besides testosterone) that are affected by the season.
Heat production in the winter: As the days get shorter, horses grow a winter coat to help protect them in the cold winters. Their metabolism also changes from stockpiling energy to expending energy, in the form of heat. Even on cold days, the horse’s body temperature remains in a tight range.
◆︎ Why do we care when the seasonal rise starts?
Some horses will get laminitis from the hormonal changes that include elevated ACTH. Although a one-time bout with endocrinopathic laminitis is distressing, one study reported that about 2/3 of a group of laminitic horses had a recurrence of laminitis within the next two years. The pain issues associated with laminitis and poor prognosis when there is severe hoof damage, leads many to chose euthanasia.
◆︎ When do these changes start?
For most horses, the rise in ACTH occurs in August, September, and October. However, in older horses the rise starts sooner, rises higher, and lasts longer. Some reports indicate that the seasonal rise starts as early as June.
When the ACTH levels remain elevated, compared to normal, it could indicate that your horse has Cushing’s Disease, also known as PPID.
◆︎ If you live in the south or in a warmer climate, does that change the seasonal fall increase in ACTH?
This question was studied and published in the AVMA Journal. They found that the ACTH didn’t rise as high in the southern latitudes, but still experienced a seasonal rise in clinically healthy horses.
This doesn’t mean that horses in the southern part of the country are safe. When the horse is no longer able to cope with the rise in hormones that include ACTH, the horse will have symptoms. While a shaggy coat is not problematic for many horses, the increased risk for laminitis exists.
◆︎ What can we do to avoid laminitis?
Awareness:
The first step is awareness as to the risk factors of insulin resistance and PPID.
Diagnosis:
If you horse is having issues, such as foot soreness, lethargy, muscle wasting, excessive thirst and urination, excessive coat length, diagnostic testing is advised. It’s important to understand the difference between insulin resistance and PPID. Your horse may have both.
Treatment:
If your horse has high insulin levels, diet, exercise (if able), and medication may be necessary.
If your horse has elevated ACTH levels, medication may be warranted.
◆︎ Q&A
☛ My horse was tested normal last year. Does that mean that I don’t need to worry?
Unfortunately, as a horse ages, the elevation of ACTH continues to progress. Horse’s health status can change over time.
☛ My horse does not have the long shaggy coat, nor laminitis, but is older. Is he/she safe?
Exaggerated rise in ACTH occurs long before coat changes. The goal is to avoid laminitis. The increase in incidence of laminitis in the fall is attributable to the horse’s inability to cope with the rise in ACTH and other hormones.
☛ My horse has been on 1 mg of pergolide for several years and has done fine. Does that mean that I don’t need to worry?
Undertreatment of ACTH can lead to laminitic episodes.
☛ I’ve heard that you need to increase the pergolide dose to account for the seasonal rise. Is that true?
Many people do increase the pergolide levels during the fall rise, to keep the ACTH in a range that they, with their vet, considers normal.
☛ Can I just wait another month and see if my horse is worse?
Yes. That would be your choice. The risk is that you could be dealing with full-blown laminitis. It’s important to remember that diagnostics take time. Getting pergolide takes time. And it takes time from first administration until you see an improvement in the condition.
◆︎ Supplements to support your horse
Pergolide has been the gold standard for treating horses for over a decade. Some people chose to support their horse with chastetree berry. It should be noted that while chastetree berry may improve symptoms in the horse, it does not lower ACTH levels.
Now is the time to be sure that your horse is in the best possible position to enter into the fall.
We do the best that we can do for our horses.
Disclaimer: Statements regarding dietary supplements have not been evaluated by the FDA and are not intended to diagnose, treat, cure, or prevent any disease or health condition.
©Joan Kulifay, MSc. 2025