A horse can have EMS without being overweight: full analysis

Version 2

A horse can have EMS without being obviously overweight, and that’s the core takeaway from a new The Horse article by Shannon Pratt-Phillips. The piece pushes back on a common shorthand that equates EMS with obesity alone, instead underscoring that insulin dysregulation is the syndrome’s defining feature and that some horses with a normal-looking body condition can still face meaningful laminitis risk. That framing is consistent with current veterinary references and consensus guidance. (thehorse.com)

That matters because obesity has long been the most visible clinical cue for EMS, particularly in ponies and easy-keeper breeds. But over time, clinicians and researchers have described a broader spectrum of disease presentation. The 2019 ECEIM consensus statement and the Equine Endocrinology Group’s updated recommendations define EMS as a collection of metabolic and clinical features with insulin dysregulation as a consistent component, not obesity as an absolute requirement. Merck’s current review makes the same point explicitly, noting that while affected horses are typically obese and regionally adipose, a lean EMS phenotype is also recognized. (academic.oup.com)

Additional reporting from The Horse adds useful context for how this shows up in practice. In a 2025 feature on the “many faces” of EMS, experts quoted by the outlet said lean animals can retain high-risk fat depots, especially along the neck and tailhead, and that regional adiposity may be more predictive than generalized body condition in some populations. That article also cited research suggesting nonobese and moderately conditioned horses can still meet EMS criteria, reinforcing the idea that veterinarians should think in terms of multiple phenotypes rather than a single classic presentation. (thehorse.com)

From a diagnostic standpoint, the research-backed message is straightforward: test, don’t guess. Cornell’s Animal Health Diagnostic Center says EMS diagnosis depends on history, physical exam, and diagnostic testing, with insulin measurement, the oral sugar test, and leptin among the recommended tools. Merck similarly emphasizes measuring insulin responses after a standardized meal or carbohydrate challenge, and recommends using postprandial insulin concentrations to monitor whether current diet and pasture access are appropriate. (vet.cornell.edu)

Expert commentary in The Horse coverage also suggests the field is moving away from a one-size-fits-all view of the disorder. Amanda Adams of the University of Kentucky’s Gluck Equine Research Center told the publication that there are “multiple phenotypes” of EMS, including lean-type horses, and that this is why diagnostic testing for insulin dysregulation is so important. The same report quoted Kathryn Burns, DVM, DACVIM, saying veterinarians need to look for regional adiposity as well as generalized obesity, particularly in higher-risk breeds. (thehorse.com)

Why it matters: For equine veterinarians, this is a reminder that a normal body condition score shouldn’t provide false reassurance. Horses with laminitis, cresty necks, tailhead fat, breed predisposition, or unexplained metabolic concerns may warrant endocrine workups even if they don’t look obese. That has implications for screening, client communication, and management planning with pet parents, especially because diet restriction, pasture access, exercise, and hoof care may need to be tailored around insulin status rather than outward appearance alone. (merckvetmanual.com)

It also intersects with another common clinical challenge: overlap with pituitary pars intermedia dysfunction. Cornell notes EMS and PPID may occur singly or together, which means age, history, and testing strategy still matter when sorting through laminitis risk and metabolic abnormalities. In practice, that makes phenotype-aware screening more important, not less. (vet.cornell.edu)

What to watch: The next step is likely broader uptake of updated EMS and insulin dysregulation recommendations, with more attention to lean and athletic horses, regional fat deposition, and dynamic testing protocols rather than body weight alone. (ebvminpractice.org)