Texas A&M Researchers Investigate Equine Cushing’s Disease’s Impact On Reproduction

Story by Courtney Price, VMBS Marketing & Communications

January 24, 2025

Researchers at the Texas A&M College of Veterinary Medicine & Biomedical Sciences (VMBS) are studying how a disease called pituitary pars intermedia dysfunction (PPID) — also known as equine Cushing’s disease — can affect reproduction in mares.

Horses with PPID are typically older and can develop a wide variety of symptoms; some of the most harmful include suppression of the immune system, the inability to process insulin, and laminitis — inflammation of horse’s hooves. 

Dr. Yatta Boakari, an equine reproduction expert and assistant professor in the VMBS’ Department of Large Animal Clinical Sciences and head of the Comparative Reproductive Laboratory, and her doctoral student, Dr. Sophia Marchio, recently published a review of around 60 studies on equine PPID in the 2024 conference proceedings for the American Association of Equine Practitioners aiming to uncover the relationship between PPID and mare fertility.

“What Sophia and I discovered is that many studies on PPID are not conducted on mares that actually have the disease, particularly in a clinical or systematic research setting,” Boakari said. “Alternatively, some studies focus on one hormone affected by PPID but do not examine how multiple overproduced hormones interact. This calls into question whether this research can reliably be used to help mares with the disease.”

“As modern medicine helps horses to live longer, PPID may become more common,” Marchio said. “If a mare appears to be perfectly healthy but is having trouble with getting pregnant or producing embryos, PPID may be the cause, and we want other veterinarians to have more information on diagnosing and managing the disease.”

Hormones And Equine Health

When an animal has PPID, it develops tumors in the pituitary gland, a part of the brain that helps regulate hormones. These tumors lead to overproduction of a hormone called ACTH, which can cause a variety of symptoms.

“One of the most recognizable symptoms is delayed shedding or a very long coat,” Marchio said. “PPID can also cause other noticeable symptoms, like muscle loss and dental problems. But the presence of symptoms varies from individual to individual, making it important to look at a horse’s health holistically before making a diagnosis.

“It’s also important to know that, despite being common in horses more than 15 years old, the disease can occur in middle-aged and even younger horses,” she said.

One of the least understood symptoms of PPID is reproductive dysfunction.

“Horses with PPID tend to be older, which already means that they are more likely to experience reproductive problems,” Boakari said. “Having PPID makes things even more complicated. As veterinarians, we need a more detailed understanding of the impacts on fertility caused by this disorder so we can ensure the well-being of equine patients.”

Currently, PPID is difficult to diagnose without bloodwork, which can detect certain key hormone levels in the blood.

“Many people associate PPID so strongly with symptoms like a long coat that they don’t suspect it of being the cause if they don’t see that particular symptom,” Marchio said. “But not all horses present this clinical sign. That’s why it’s important to consider the horse’s entire health history.”

To continue their investigation, Boakari and Marchio plan to use RNA sequencing to better identify the differences between genes in the uteruses of healthy mares to those with PPID.

“This will help us understand why these mares might have fertility issues,” Boakari said.

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For more information about the Texas A&M College of Veterinary Medicine & Biomedical Sciences, please visit our website at vetmed.tamu.edu or join us on Facebook, Instagram, and Twitter.

Contact Information: Jennifer Gauntt, Director of VMBS Communications, Texas A&M College of Veterinary Medicine & Biomedical Sciences, jgauntt@cvm.tamu.edu, 979-862-4216

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