PPID affects up to 30% of older horses, causing a range of problems, from poor performance to severe illness and even death. The disease occurs when neurons in the hypothalamus are damaged, disrupting the brain’s ability to regulate the pars intermedia region of the pituitary gland. While there is no cure, treatment focuses on managing symptoms and slowing progression.
The most widely used treatment is pergolide which helps compensate for the dopamine loss seen in affected horses. Originally developed for Parkinson’s disease in humans, pergolide remains the only FDA-approved drug for PPID in horses.
However, horses vary widely in how they respond to this medication. Studies show that 60 - 80% of horses respond well, but definitions of “success” differ. Moreover, adverse effects are common. Anorexia is reported in up to 32% of treated horses, alongside issues like colic, weight loss, and behavioural changes. These side effects often lead owners or veterinarians to reduce or stop treatment, allowing the disease to worsen.
In human medicine, it is well established that genetic differences can influence how individuals respond to drugs. Researchers now believe the same may be true for horses.
To explore this, Dr. Molly McCue and Dr. Lauren Hughes of the UMN Equine Genetics and Genomics Laboratory, together with Dr. Dianne McFarlane at the University of Florida, are leading a study to identify genetic factors that influence pergolide response and side-effect risk in horses with PPID.
“Our goal is to identify genetic variants that influence treatment outcomes,” explain the researchers. “If we can find alleles that predict poor response or higher risk of adverse effects, we could tailor dosing and treatment to each horse, making therapy safer and more effective.”
Dr. Hughes adds, “As a veterinarian, I’ve seen how devastating PPID can be for horses and their owners. This research could help us greatly improve diagnosis, treatment, and management of this disease.”
The team is seeking horses diagnosed with PPID by a veterinarian - confirmed through bloodwork - who have been on pergolide therapy for at least six months. They are particularly interested in horses that:
· Require higher or more frequent doses of pergolide
· Experience adverse effects such as appetite loss, weight loss, colic, or behavioural changes
Eligible horses should:
· Be 15 years or older at the time of diagnosis
· Have clinical signs consistent with PPID (e.g. long, shaggy coat, muscle loss, dullness, or recurrent infections)
· Have had follow-up blood tests (ACTH, TRH stimulation, or dexamethasone suppression tests)
Participation involves submitting medical records and providing hair root or blood samples. Owners may enrol as many horses as they wish.
The researchers emphasise that participation is vital: by contributing samples and data, owners will help uncover the genetic clues that could shape the future of personalised PPID treatment - offering hope for safer and more effective therapies for horses everywhere.
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