The Seasonal ACTH Rise

ACTH, adrenocorticotropic hormone, is produced by the pituitary gland. It’s function is to trigger cortisol release from the adrenal gland.  Every year in the fall there is a temporary increase in the amount of ACTH produced. For most horses this is a relatively small increase and does not cause any problems.  However, for horses in the early stages of PPID [pituitary pars intermedia dysfunction, aka Cushing’s Disease], it can mean disaster.

Autumn is dangerous for horses with undiagnosed early PPID

The classical and most obvious outward signs of PPID are muscle wasting, sagging abdomen and a long, often curly coat that does not shed normally.  However, these develop relatively late in the course of the disease and PPID  can be present for many years before they are seen.

Abnormally  high ACTH levels are a laboratory marker of PPID but in early cases may be normal for most of the year. When the seasonal ACTH rise hits, these early PPID cases go into overdrive and generate levels much higher than the usual rise in healthy horses.

ACTH stimulates the adrenal gland to produce cortisol. Cortisol in turn causes insulin resistance. This can result in an unexpected case of laminitis, often the first of the horse’s life. Horses that already are EMS cases are at particularly  high risk of developing insulin levels high enough to cause laminitis but it can happen  to horses without a history of EMS too.  An unexplained autumn laminitis is often the very first sign of PPID.

There are some other signs of an abnormally high ACTH rise. Look for:

  • Sudden increased water consumption (often doubles)
  • Increased urination
  • Filling of the fossae above the eyes with fat
  • Development of a fatty crest – or worsening if already there

The seasonal ACTH rise starts with minor increases that ramp up slowly starting end of June. The upward climb accelerates in September and peaks last week in September, with some minor variability depending on exact geographical location. Horses in the early stages of PPID experience exaggerated rises and problematic levels can be found as early as July in some horses.

If you see signs suggesting ACTH elevation may be excessive, call you veterinarian and do blood work to check. It may be suggested to start treatment with pergolide even before the blood results are in. Its important to understand the laminitis and other changes can only be controlled by removing the cause – the high ACTH. That is what the pergolide does.  No amount of diet manipulation, supplements or anti-inflammatory drugs is going to make a difference if you don’t address the root cause.

If your horse is in his/her teens or older and develops unexplained laminitis in late summer/fall, be sure early PPID is on your list of possible causes and check ACTH. A correct diagnosis is the road to correct treatment.

Eleanor Kellon, VMD


About Dr. Kellon

Graduate of University of Pennsylvania Veterinary School. Owner of Equine Nutritional Solutions,, industry and private nutritional consultations, online nutritional courses. Staff Veterinary Expert at Uckele Health and Nutrition.
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7 Responses to The Seasonal ACTH Rise

  1. Renae says:

    I have a miniature that has not been on grass for about 6 years. He gets only hay and Alfalfa/Timothy pellets. He has an episode ever year around the end of August when his hair starts growing back in. It last about a month of lameness. Could this be Cushings as well?. He was tested but it was negative,

    • Dr. Kellon says:

      Yes, it could be. If he tests normal, repeating it in September may show an exaggerated rise. Otherwise, you can wait until December and test him with the more sensitive TRH stimulation test. Some early cases only need medication during the seasonal rise.

  2. Susan hidalgo says:

    Consider no grain intake. Instead feed ration balancer, i.e., purina plus 32. Consult with vet for his or her recommendation. Avoid weeds as they typically double sugar.

  3. Chris McSherry says:

    What else can I do? In April I realized my 30 YO IR mare has classic signs of PPID; put her on 1mg of Prascend & doing great. 22YO Mustang mare with no (visible) previous health issues of any kind (have had her for 20 years) – PPID positive, terrible hoof pain, laminitic, all of it. 1.5 mg Prascend + Uckele Jiaogulan which visibly helps. On a “paddock paradise” track, minerals balanced as per your class, served with 1/2 cup moistened timothy pellets. She eats & drinks well; fat for the first time in her life; mobile but painful & stiff legged; dropped soles below the toe in front; alert and curious and delighted to see me… but when suffering overtakes that sparkle… How else can I intervene? Thank you.

    • Dr. Kellon says:

      The seasonal ACTH rise is not influenced by diet. You are thinking of insulin.

      • Chris McSherry says:

        Thank you for telling me that. I thought it was the overall picture, not JUST the pituitary (and the ACTH) that caused/worsened/managed the Cushings. She was not discernibly IR nor laminitic at any time prior until the PPID became obvious, though as you indicate either can be subtly present for a long time. At any rate, I lost Rachael three days after writing to you: her pain was such that she could not bear to keep her BACK feet on the ground. Her condition deteriorated very rapidly.

    • Dr. Kellon says:

      Chris: If you have checked ACTH to make sure the pergolide dose is adequate the missing link is often the trim. Join

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