horses respond to treatment for pituitary pars intermedia dysfunction (PPID), commonly known as equine Cushing’s disease. This condition, which affects up to 30% of older horses, can have serious consequences ranging from diminished performance to death.
PPID develops when neurons in the hypothalamus become damaged, resulting in the loss of control over the pituitary gland’s pars intermedia. While there is currently no cure, treatment focuses on slowing disease progression and managing clinical signs. The gold-standard medication for PPID is pergolide, a dopamine receptor agonist originally used to treat Parkinson’s disease in humans. Pergolide helps compensate for dopamine loss in hypothalamic neurons and is the most widely prescribed drug for PPID.
However, horses vary significantly in their response to pergolide. Treatment success rates are reported to range from 60–80%, but comparisons across studies are difficult due to differing definitions of “success.” Additionally, adverse effects are relatively common, with some studies reporting anorexia in up to 32% of treated horses. Other side effects may include colic, weight loss, and behavioural changes. These reactions often lead owners or veterinarians to reduce or discontinue treatment - causing symptoms to return or worsen and allowing the disease to progress.
It is well established in human medicine that genetic differences can influence how individuals respond to medications. Now, the same principle is being explored in horses.
The study, led by Dr. Molly McCue and Dr. Lauren Hughes from the UMN Equine Genetics and Genomics Laboratory, in collaboration with Dr. Dianne McFarlane from the University of Florida, aims to uncover genetic factors that affect pergolide response and adverse event susceptibility in horses with PPID.
“Our goal is to identify genetic variants that influence treatment outcomes,” explain the researchers. “If we find specific alleles that predict poor response or higher risk of side effects, this could lead to more personalised treatment—such as adjusted dosing strategies to improve safety and effectiveness.”
“As a veterinarian, I understand just how devastating PPID can be for horses and the owners that love them,” said Dr. Hughes in a UMN College of Veterinary Medicine news release. “I’m very excited about the potential of this research to improve how we diagnose, treat, and manage this important disease.”
The research team is actively seeking suitable horses to enrol in the study. They are looking for horses that meet the following criteria:
- Over the age of 15 at time of PPID diagnosis
- Diagnosis made by veterinarian and diagnosis included bloodwork
- Horse has/had clinical signs consistent with PPID (long shaggy haircoat, muscle atrophy, changes in mentation, or recurrent infections)
- Horse has been on pergolide therapy for a minimum of 6 months and has had recheck blood values (including ACTH, TRH stim, or dexamethasone suppression blood work)
If your horse meets the criteria, you are encouraged to participate. Your involvement is essential - this research would not be possible without the support of dedicated horse owners and their animals.
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