Some horse breeds are more prone to metabolic diseases, specifically pituitary pars intermedia dysfunction (PPID) and insulin dysregulation (ID).

One presentation at the 5^th Global Equine Endocrine Symposium (GEES) presented by Boehringer Ingelheim, held in January 2023, discussed pituitary pars intermedia dysfunction (PPID or equine Cushing’s disease) and insulin dysregulation (ID) in horse breeds classified by genetic clade. (The research was titled Prevalence of Pituitary Pars Intermedia Dysfunction and Insulin Dysregulation in Horse Breeds Classified by Genetic Clade, and it was authored by Rachel Lemcke, MS, of Amwell Data Services LLC, in New Jersey; and Steve Grubbs, DVM, PhD, DACVIM, and Kelly Graber of Boehringer Ingelheim Animal Health USA.) 

This retrospective analysis was performed on veterinarian-provided data from a 2016-2020 study in the United States on 6,266 ponies and horses with suspected endocrine disorders (primarily PPID, also called Cushing’s disease). This study did not include Quarter Horses or Paints due to the high risk of breed misclassification.

The enrolled horses were separated by breed into 13 clades, which is a branch of a genetic cladogram that includes a single common ancestor and all of that individual’s descendants. Several clades included closely related breeds. Frequency of endocrine-associated clinical signs were also compared among endocrine classifications and clades.

PPID and ID in Horse Breed Clades

The research showed that both the highest rates of PPID (61.52%) and insulin dysregulation (ID) (72.22%) occurred in Clade 3, which included Miniature Horses, Shetland ponies and dwarf ponies.

The lowest rate of PPID (21.70%) was found in Clade 2 (Lusitano and Andalusian).

Clade 7 (Percheron and Belgian Draft) had the lowest rate of insulin dysregulation (24.84%).

In addition, endocrine disorders were identified in more than half the horses 10 years old and younger in the majority of clades, highlighting the need for endocrine testing in younger horses.

Decreased athletic performance was not statistically associated with any endocrine classification or combination evaluated.

Laminitis, however, was statistically associated with horses that had both PPID and insulin dysregulation, as well as those with insulin dysregulation only.

Clade 1 (Peruvian Paso and Paso Fino) and Clade 3 (which included Miniature Horses, Shetland ponies and dwarf ponies) had statistically higher rates of laminitis than several other clades.

Horses in this data set were more likely to have both PPID and insulin dysregulation rather than only PPID. In fact, horses were more likely to have only insulin dysregulation or no identified endocrine disorder than to only have PPID.

It is important to note that the majority of these horses and ponies were not tested using dynamic testing, suggesting these frequencies of endocrine disorders might be underestimated.

What You Need to Know About Equine PPID and ID

This research highlights the continued need for horse owners to have their veterinarians evaluate younger and older horses and ponies for endocrine disorders when the animals have clinical signs. Preferably the veterinarians would use dynamic testing (which is more sensitive than static testing).

Testing for only one endocrine disorder (e.g., PPID or ID) might lead to an oversimplification of the endocrine dynamic within patients. This means the testing could inadvertently allow undiagnosed endocrine comorbidities to cause further clinical signs and negatively impact the health of the horse or pony.

This research can help inform veterinarians and horse owners of the likelihood of endocrine disorders within specific horse and pony breeds.

Editor’s note: You can access the full Proceedings of the 5th GEES Symposium here.