Case studies over more than a decade suggest that while pergolide does not seem to prolong life, it does improve quality of life over prolonged periods. And, in general, horse owners are very satisfied with long-term pergolide treatment, said Harold C. Schott II, DVM, PhD, Dipl. ACVIM, a professor in equine internal medicine at Michigan State University, in East Lansing.

“As we all know, PPID is increasingly being recognized and treated, and we’re trying to make those longer-term treatment decisions, because the financial implications can be challenging with our individual clients,” said Schott, speaking at the 2022 American Association of Equine Practitioners (AAEP) Convention, held Nov. 18-22 in San Antonio, Texas.

Veterinarians frequently prescribe pergolide to treat PPID horses, but very little research into the long-term effects of such treatment exists, Schott said.

Since 2009, Schott and his fellow researchers have been following the health status of 28 horses and two ponies from the time they first received pergolide for PPID until the ends of their lives. They have averaged 23.1 years in age at the start of treatment, based partly on age estimations for some of the equids.

Half the animals started out on a dose of 1 milligram per day, and the other half started with twice that amount, he said. The researchers examined each horse or pony after 2.5, 3, 3.5, 4.5, 5.5, 6.5, 9.5, and 12.5 years of treatment. They interviewed the animals’ owners every three months.

On average, the equids have survived a little more than three years, he said. But survival times have varied widely, from seven months to 12.5 years following the initiation of pergolide. One of the 30 equids initially enrolled in the study is still thriving.

Five horses were euthanized due to PPID-related laminitis, he said. The other 24 were euthanized or died due to diseases common in aging equids.

Seven of the animals that originally started on a relatively low dose had it increased to 2 milligrams per day after the first two to five years. But overall, the equids showed ongoing improvement in clinical signs over the years. Even after five and a half years, owners reported that the 13 surviving equids continued to improve, showing a better hair coat, improved energy levels, better appetite, and less frequent bouts of laminitis. Three-fourths even had normal endocrine test results, Schott said.

“This was quite surprising to me, that after prolonged use we saw this improvement,” he said.

Even so, only two of the remaining six equids had normal endocrine tests four years later, he added.

In general, owners were very pleased with the effects of pergolide in their PPID horses, said Schott.

After 10 years of treatment, 71% of horse owners strongly agreed and an additional 25% agreed that the drug improved their horses’ quality of life. Further, 88% of owners agreed or strongly agreed they would provide lifelong treatment. Nearly three-fourths of the owners were willing to invest at least $1,000 per year in pergolide treatment for the duration of their animal’s life.