South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
Fat, foundered horses: Equine Metabolic Syndrome and laminitis
Schott HC*
Professor, Equine Internal Medicine
Department of Large Animal Clinical Sciences
D-202 Veterinary Medical Center
Michigan State University, East Lansing, MI 48824-1314
(517)-353-9710 [email protected]
Middle-aged obesity (body condition score [BCS] 7-9 on a scale of 1 to 9) accompanied by
insidious-onset laminitis is a syndrome that has been recognized by equine practitioners for
decades. Equine metabolic syndrome (EMS) is the name that has gained acceptance to describe
this condition. Clinical signs of laminitis commonly develop while horses are grazing spring
pasture but can also occur at other times of the year and in horses without pasture access. Affected
horses tend to be aged between 10-to-20 years and there does not appear to be a sex predilection.
Occasionally, the syndrome can occur in younger animals that have been overfed. Pony breeds,
domesticated Spanish mustangs, Peruvian Pasos, Paso Finos, Andalusians, European
Warmbloods, American Saddlebreds, Arabians, and Morgan horses are more commonly affected
than Thoroughbreds, Standardbreds, and Quarter Horses. This breed disparity is supportive of a
genetic predisposition. In the past, this syndrome was commonly attributed to hypothyroidism or
pituitary pars intermedia dysfunction (PPID or classic equine Cushing‟s disease); however, most
affected horses do not manifest additional clinical signs or endocrinologic test results to support
these conditions. It is now recognized that insulin resistance (IR) is the primary endocrinopathy
induced by obesity in EMS-affected horses. However, a number of additional metabolic and
endocrinologic alterations can occur in affected equids making the pathophysiology of EMS an
increasingly complex subject. Finally, a subgroup of EMS-affected equids may only have
abnormal fat deposits (e.g., a cresty neck or fat deposits behind the shoulders, over the tail head,
and in the sheath of male horses) without generalized obesity and these patients are often more
challenging to manage than those with generalized obesity.
Prevalence of laminitis and obesity in horses: Laminitis is a devastating clinical problem for
horses and their owners. In fact, data collected in the 2000 USDA-NAHMS study revealed that
laminitis was reported on 13% of horse operations. Further, the leading cause of laminitis was
reported to be grazing lush pasture (Figure 1). Similarly, in the United Kingdom more than 8,000
cases of laminitis are estimated to occur annually, representing 7% of the equine population, and
more than 60% of cases were classified as pasture-associated disease. In both reports, pastureassociated laminitis had a peak incidence in May, followed by October and November.
As horses have transitioned from beasts of burden to recreational companions, the physical
condition of many horses has paralleled that of their human counterparts: they have been overfed
and become more sedentary. As a consequence, obesity is becoming a significant problem in the
equine species. In recently studied cohorts of horses in Ohio and Virginia, nearly 20% were
classified as obese, defined as a BCS >7.5, and 50% were considered overweight.
50