Lean horses can still have equine metabolic syndrome
Bottom line
Version 1
Horses can have equine metabolic syndrome, or EMS, even when they aren’t obviously overweight, according to a new explainer in The Horse and broader endocrinology guidance reviewed for this story. The key issue isn’t body weight alone, but insulin dysregulation, which is the defining feature of EMS and the main driver of hyperinsulinemia-associated laminitis. While many affected horses are obese or overconditioned, veterinary references and updated expert guidance now explicitly describe a “lean phenotype,” in which horses maintain a normal body condition score but still show abnormal insulin responses, regional fat deposits, or a history consistent with laminitis risk. (thehorse.com)
Why it matters: For equine practitioners, the takeaway is that a normal-looking horse shouldn’t be ruled out for EMS if the history, breed, hoof changes, or fat distribution raise concern. Current guidance emphasizes that obesity is not required for diagnosis, and that testing should focus on documenting insulin dysregulation rather than relying on condition score alone. That matters because laminitis risk can remain high in non-obese horses, especially in “thrifty” breeds and ponies, and management may need to center on low-nonstructural-carbohydrate forage, grazing restriction, exercise when safe, and ongoing metabolic monitoring rather than simple weight-loss plans. (merckvetmanual.com)
What to watch: Expect continued attention on earlier screening for insulin dysregulation, plus growing interest in adjunct therapies such as SGLT2 inhibitors for refractory cases. (thehorse.com)
Version 2
A horse doesn’t have to be overweight to have EMS, and that’s the core message emerging from a recent The Horse explainer by equine nutrition researcher Shannon Pratt-Phillips, PhD, alongside updated veterinary guidance on equine endocrine disease. Across sources, the shift is clear: EMS is increasingly framed less as an obesity-only syndrome and more as a disorder defined by insulin dysregulation and laminitis risk, including in some horses that appear to be at a healthy weight. (thehorse.com)
That reflects a broader evolution in how the profession talks about EMS. Historically, EMS was closely associated with the classic “easy keeper” phenotype: obese ponies or horses with cresty necks, regional adiposity, and recurrent laminitis. But more recent consensus materials from the Equine Endocrinology Group, echoed in Merck Veterinary Manual and AAEP educational content, distinguish between obese EMS and non-obese EMS, with insulin dysregulation as the common denominator. In other words, excess fat is typical, but it’s no longer treated as essential for the diagnosis. (merckvetmanual.com)
The clinical reason for that distinction is laminitis. Merck states that insulin dysregulation is the core component of EMS and that high insulin concentrations are what lead to hyperinsulinemia-associated laminitis. Its current review notes that affected animals are often obese, but also explicitly says a lean EMS phenotype is described. The same source warns that obesity and a cresty neck are not enough to confirm EMS, and, just as importantly, the absence of obesity is not enough to exclude insulin dysregulation. (merckvetmanual.com)
That aligns with the 2024 Equine Endocrinology Group recommendations, which outline non-obese EMS as a recognized category and place insulin testing at the center of diagnosis and follow-up. The practical implication is that veterinarians should pay closer attention to signalment, hoof history, regional adiposity, and metabolic testing in horses that may otherwise “look normal.” UC Davis similarly notes that EMS often affects “thrifty” equids, including ponies, donkeys, Arabians, and mustangs, and emphasizes diet and exercise management, with exercise deferred when laminitis is active. (idppid.com)
Industry and expert commentary also suggest the management conversation is changing. Pratt-Phillips’ piece for The Horse is aimed at answering a question many pet parents and barn managers still ask: can a horse with a normal body condition really be metabolically compromised? The answer, based on current guidance, is yes. Meanwhile, Nancy S. Loving, DVM, writing in EquiManagement about updates in PPID and EMS, highlights the same expanding understanding of endocrine disease, including hyperinsulinemia-associated laminitis and newer treatment discussions such as SGLT2 inhibitors. A 2024 review indexed in PubMed likewise describes SGLT2 inhibitor use as an emerging management option in ponies and horses with insulin dysregulation, particularly when conventional measures fall short. (thehorse.com)
Why it matters: For veterinary professionals, this is a reminder to avoid using body condition score as a screening shortcut. A horse with a normal topline and acceptable overall condition can still have regional fat deposits, an exaggerated post-prandial insulin response, prior subclinical laminitis, or breed-linked metabolic risk. That changes case finding, client communication, and monitoring. Instead of reassuring pet parents based on appearance alone, clinicians may need to recommend targeted endocrine workups, especially in horses with laminitic episodes, divergent hoof rings, cresty necks without generalized obesity, or a history suggesting they are unusually efficient keepers. (merckvetmanual.com)
It also complicates management in a useful way. In obese EMS cases, the plan often centers on weight reduction alongside low-NSC feeding. In lean EMS cases, the goal is different: maintain an appropriate body condition while reducing insulin and laminitis risk. That means precise forage selection, tighter control of starch and sugar intake, cautious pasture access, and exercise plans tailored to hoof status, rather than simply feeding less. As newer therapies are explored, including SGLT2 inhibitors for refractory insulin dysregulation, veterinarians may have more tools, but the diagnostic burden up front becomes more important, not less. (merckvetmanual.com)
What to watch: The next step for the field is likely broader adoption of insulin-focused screening algorithms, plus more real-world data on when newer pharmacologic options should complement, rather than replace, diet, exercise, and hoof-care management. (idppid.com)
Common questions
Can a horse have EMS without being overweight?
Yes. The article says EMS can occur in horses that appear to be at a healthy weight, because insulin dysregulation, not body weight alone, is the defining feature.What signs can suggest EMS in a normal-looking horse?
Regional adiposity, a cresty neck, hoof changes, a history of laminitis, or an abnormal insulin response can all raise concern, even if body condition looks normal.What should veterinarians focus on when testing for EMS?
Testing should document insulin dysregulation rather than relying on body condition score alone.How is lean EMS managed?
The article says management may focus on low-nonstructural-carbohydrate forage, tighter control of starch and sugar intake, grazing restriction, exercise when safe, and ongoing metabolic monitoring.