Lean horses can still have equine metabolic syndrome
Bottom line
A new clinical explainer in The Horse is reminding veterinarians and pet parents that equine metabolic syndrome, or EMS, doesn't require generalized obesity to be present. Shannon Pratt-Phillips, MSc, PhD, wrote that horses with a normal body condition score can still have insulin dysregulation, the hallmark feature of EMS, and that regional fat deposits, diet high in nonstructural carbohydrates, and genetic predisposition can all contribute to risk. That framing aligns with recent reviews and guideline updates, which emphasize that obesity is common in EMS, but not universal, and that lean horses can still develop hyperinsulinemia-associated laminitis. (thehorse.com)
Why it matters: For veterinary professionals, the takeaway is practical: body condition alone isn't enough to rule EMS in or out. Recent reviews recommend objective testing for insulin dysregulation, especially dynamic testing such as the oral sugar test, because basal insulin can miss cases. That matters for laminitis prevention, since persistent or exaggerated hyperinsulinemia, not simply excess weight, is the core risk factor clinicians are trying to detect and manage. (beva.onlinelibrary.wiley.com)
What to watch: Expect continued focus on earlier metabolic screening, breed-specific risk assessment, and individualized management plans for lean versus obese horses with EMS. (bvajournals.onlinelibrary.wiley.com)
Key facts
- Topic
- Equine metabolic syndrome can occur without generalized obesity.
- Defining feature
- Insulin dysregulation is the hallmark feature of EMS.
- Risk factors
- Regional fat deposits, high nonstructural carbohydrate intake, and genetic predisposition.
- Diagnostic takeaway
- Body condition alone is not enough to rule EMS in or out.
- Testing recommendation
- Objective insulin testing is recommended, especially the oral sugar test.
- Basal insulin testing
- Basal insulin can miss cases.
- Laminitis risk
- Persistent or exaggerated hyperinsulinemia is the core risk factor for laminitis.
- Article date
- April 23, 2026
A fresh article in The Horse is putting a finer point on a message equine internists have been sharpening for years: yes, a horse can have equine metabolic syndrome without being overweight. In the April 23, 2026 piece, nutrition researcher Shannon Pratt-Phillips said horses with a healthy body condition can still develop EMS, because insulin dysregulation, not obesity itself, is the syndrome's defining feature. (thehorse.com)
That message reflects how the field's understanding of EMS has evolved. Earlier descriptions often centered on the classic overweight, easy-keeper phenotype, but more recent reviews and recommendations define EMS as a cluster of metabolic and clinical features in which insulin dysregulation is the consistent component driving laminitis risk. The Equine Endocrinology Group's updated recommendations and multiple 2026 reviews now explicitly note that obesity is frequent, but not required, and that not all obese horses are metabolically abnormal. (ebvminpractice.org)
In The Horse, Pratt-Phillips explained that even leaner horses may carry regional adiposity, such as fat along the neck or tailhead, that could still be metabolically relevant. She also pointed to diet, especially high starch and sugar intake, and genetics as contributors to insulin dysregulation. Those points line up with a 2026 In Practice review, which says high-nonstructural-carbohydrate diets can reduce insulin sensitivity, and that certain breeds appear overrepresented, with emerging genomic work suggesting multifactorial inherited risk. (thehorse.com)
Recent literature has also made the diagnostic implications clearer. In a 2026 Equine Veterinary Education review, François-René Bertin wrote that EMS can occur in lean animals and therefore requires objective diagnostic testing rather than reliance on body condition alone. The same review highlights that basal insulin testing is specific but relatively insensitive, while dynamic testing, particularly the oral sugar test, is more reliable for identifying exaggerated postprandial insulin responses and estimating laminitis risk. (beva.onlinelibrary.wiley.com)
Industry coverage is echoing that shift. In a June 2026 EquiManagement report on an equine endocrinology webinar, Kelsey Hart, DVM, PhD, DACVIM, described EMS as a disorder that can occur at any age and in as many as 50% of predisposed breeds, with both genetic and environmental drivers. Hart also tied insulin dysfunction directly to hyperinsulinemia-associated laminitis, reinforcing that clinicians should think beyond visible obesity when screening at-risk horses. (equimanagement.com)
Why it matters: For veterinary professionals, this is less about a new discovery than a clinical correction that can change case finding. If practitioners and pet parents still associate EMS mainly with obvious obesity, lean horses with recurrent foot soreness, subtle regional fat deposits, breed predisposition, or unexplained insulin abnormalities may be screened too late. That has consequences because endocrinopathic laminitis is strongly linked to persistent hyperinsulinemia, and recent reviews note that some cases may be subclinical before overt lameness appears. Earlier metabolic testing can help practices intervene with diet, exercise, pasture management, hoof monitoring, and, in refractory cases, adjunct pharmacologic options. (pubmed.ncbi.nlm.nih.gov)
The nuance also affects management. Reviews published in 2026 note that dietary recommendations differ for obese and lean EMS cases, meaning the goal isn't indiscriminate weight loss in every horse with insulin dysregulation. Instead, clinicians need individualized plans that restrict nonstructural carbohydrates, manage pasture exposure, and preserve appropriate body condition while improving insulin control. That distinction is especially important when communicating with pet parents, who may falsely assume a horse at an ideal weight is metabolically safe. (bvajournals.onlinelibrary.wiley.com)
What to watch: The next phase is likely to be more precise screening and management, including broader use of dynamic insulin testing, closer monitoring of predisposed breeds and older horses, and more discussion around when adjunct therapies such as SGLT2 inhibitors belong in difficult EMS cases. (equimanagement.com)