Pituitary pars intermedia dysfunction (PPID), equine metabolic syndrome (EMS), and insulin dysregulation (ID) are three endocrine disorders that can develop in older horses. Because they can be confusing to understand, Edd Knowles, MA, PhD, VetMB, MVetMed, Dipl. ECEIM, MRCVS, director of science and nutrition at Mars Horsecare, described the key differences between them. 

Insulin Dysregulation 

In horses, ID means insulin levels are too high, either at baseline (when the horse hasn’t eaten anything) or post-feeding. It can also mean the horse’s tissues don’t respond normally to the hormone insulin. 

Equine Metabolic Syndrome 

Horses with EMS display a variety of clinical signs, including insulin dysregulation. Essentially, said Knowles, the term describes the fact that we often see ID together with other features, including obesity, fat accumulations in certain areas, increasing age, and in certain breeds.  

“It’s really important to remember that whilst these things often happen together, they don’t always happen together,” said Knowles. “We see horses with high insulin levels that are thin, that are young, and of all different breeds and types. So it’s important to remember that these things are clues.”  

He added that EMS also describes the fact that horses with high insulin levels are more likely to develop the debilitating hoof disease laminitis. 

Pituitary Pars Intermedia Dysfunction 

With PPID, part of the pituitary gland at the base of the brain is behaving abnormally.  

“It usually means that that part of the brain is enlarged and is producing higher levels of hormones, and it produces a wide variety of different hormones,” said Knowles. “Those hormones can then go on to cause symptoms in the horses, which we’ll see and recognise as the signs of PPID.” 

Horses with PPID might or might not have insulin dysregulation. “It is likely that PPID can contribute to making that insulin dysregulation worse when we get the two things happening together,” he added. 

Take-Home Message 

PPID, EMS, and ID are three different terms that describe three different things. “Insulin dysregulation, from a practical perspective in horses, means insulin levels are too high at some parts of the day,” said Knowles. “Equine metabolic syndrome just describes the fact that we often see insulin dysregulation in certain types of horses and in association with laminitis. And finally, PPID really describes what the pituitary gland is doing. That term itself doesn’t tell us anything about the insulin state of that horse.”  

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  • Alexandra Beckstett is a lifelong horse owner and an award-winning writer and editor. She is the editorial director of EquiManagement and MyNewHorse.com, prior to which she spent 13 years with The Horse/TheHorse.com.

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