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Veterinarians frequently prescribe pergolide for horses and ponies diagnosed with pituitary pars intermedia dysfunction (PPID). In fact, it is considered the drug of choice for treating the disease. One side effect of pergolide, however, is a sluggish appetite and lethargy.

“The recommended dose for horses starts at 0.001 mg/kg/day orally, which equates to about 0.5 mg for an average horse. Some ponies have success on 0.25 mg/day,” said Laura Petroski, a veterinarian for Kentucky Equine Research. “Clinical improvement should be noted within a few weeks. If no improvement is observed, the dose is increased by 0.001 mg/kg until clinical signs fade. The maximum dose is 0.010 mg/kg.”

PPID-affected horses release inconsistent amounts of dopamine in their brains. Because dopamine controls most physiological pathways, veterinarians often see systemic issues in horses with fluctuating dopamine levels.

“Pergolide is a dopamine agonist, which is a drug that behaves like a dopamine molecule. The chemical makeup of this drug is so similar to dopamine that it is able to bind to dopamine receptors, thus rectifying the issues observed with low levels of dopamine in the brain. Due to the increased presence of dopamine agonists with pergolide therapy, there is an upregulation of dopamine receptors in the brain. This increase in dopamine receptors has been linked to low motivation for feed,” explained Petroski.

Because of this, many horses experience reduced appetite or anorexia once treatment with pergolide has begun, but appetite typically returns to normal as the animal acclimates to the new drug. Normal appetite will return only if the animal is on the correct dosage, though. If inappetence lasts longer than a week or 10 days, the usual recommendation is to reduce the pergolide in 0.001 mg/kg increments, according to Petroski.

Once clinical signs have been successfully controlled by pergolide, owners are advised to run blood tests on their horse two to four times per year and to monitor their horses for any signs of deterioration. “Although horses with PPID need medical management their entire lives, some horses remain stable on doses lower than the recommended starting dose,” explained Petroski.

Owners of PPID horses should keep a close eye on horses as they begin pergolide therapy. In an effort to stave off inappetence, they should offer meals that horses are familiar with and consume readily. While it is tempting to overhaul a diet as soon as the diagnosis of PPID is made, introducing new feedstuffs and pergolide at the same time is probably not wise, particularly if the horse is a picky eater. Instead, acclimate the horse to pergolide, adjust the dosage if necessary under the direction of a veterinarian, and then slowly introduce new feedstuffs only after the horse is again eating well.

Not all horses experience depressed appetite when they begin pergolide, but many do, and it is best to be well informed of this side effect.

Working closely with a veterinarian will give a horse diagnosed with PPID the best chance at a normal life. Do you need help formulating a diet for your PPID horse? Kentucky Equine Research can help. Send us a note today!

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