Scientists have long considered obesity to be a primary driver of equine metabolic syndrome (EMS). If this is true the horse industry is facing a very big problem; in a recent study of 300 horses in Virginia, researchers found that 51% of them were obese. That means more than half the country's horse population is at risk of EMS and, thus, laminitis, right? Not so fast.
Ray Geor, BVSc, PhD, Dipl. ACVIM, a professor and researcher at Michigan State University (MSU), presented an overview of recent EMS research at the 2013 International Equine Conference on Laminitis and Diseases of the Foot, held Nov. 1-3 in West Palm Beach, Fla. In particular, he discussed a recent study headed by researchers at the University of Minnesota (Nichol Schultz, DVM; Molly McCue, DVM, MS, PhD, Dipl. ACVIM; and Krishona Martinson, PhD) in collaboration with MSU (Geor) and Tufts University (Nicholas Frank, DVM, PhD, Dipl. ACVIM). With this study they aimed to better define the physical and metabolic characteristics of EMS in an effort to better diagnose, manage, and prevent the disease and associated laminitis cases.
The first EMS feature of Geor described was insulin resistance (IR), a reduction in a horse’s sensitivity to the hormone insulin that makes it harder for cells to transport glucose (sugar) out of the bloodstream and store it as glycogen (energy).
"Although our understanding of the etiology and pathophysiology of EMS is far from complete, it seems likely that IR and/or associated hyperinsulinemia play an important role," he said. He cited a number of studies in which researchers have shown hyperinsulinemia, or exaggerated increases in blood insulin levels to feeding, to be a feature of the EMS phenotype (physical traits) in ponies and horses.
Next, Geor talked about obesity, defined in horses as a body condition score (BCS) of 7 or higher on the 1-9 Henneke scale. "Anecdotally, horses and ponies diagnosed with EMS may be obese and/or have regional fat accumulation, including in the nuchal ligament region (cresty neck), behind the shoulder, around the tailhead, and in the preputial or mammary gland regions," he said. "In published studies, high BCS and measures of apparent neck crest fat accumulation, including the neck circumference to height ratio, have been associated with the EMS phenotype."
Recent study results, however, have indicated that obesity is not a consistent feature in EMS. "Not all affected animals express obesity or regional adiposity; conversely, not all obese animals appear to be at increased risk for laminitis," he explained. On the other hand, increased serum insulin and triglyceride (fat) concentrations were consistently elevated in horses and ponies with a history of laminitis, regardless of their body condition. This confirms previous findings regarding insulin levels, said Geor, but indicates that elevated serum triglycerides might be another key feature of EMS.
From these study results Geor established two implications for indentifying and managing EMS: "First, the presence or absence of obesity cannot be used as the sole diagnostic criterion; instead, it is important for veterinarians to evaluate other components of EMS such as insulin response and serum triglyceride concentrations.
"Second, whereas dietary restriction and weight loss may result in some improvement in metabolic abnormalities (e.g., lower insulin concentrations) in affected animals, the underlying metabolic dysfunction is likely to persist."
So while owners should take steps to curb obesity in their horses, Geor said it is unlikely that every obese horse is also at risk of developing EMS and associated laminitis.
The study," Current understanding of the equine metabolic syndrome phenotype," was published in the October 2013 issue of the Journal of Equine Veterinary Science.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.