Equine metabolic syndrome: How can we intervene earlier?

Equine metabolic syndrome: How can we intervene earlier?

PhD student earns one of two inaugural EQUUS Foundation Research Fellows with this line of research
Mar 01, 2012

Last November during the Frank J. Milne State-of-the-Art Lecture at the 57th Annual American Association of Equine Practitioners (AAEP) Convention, Oklahoma State University PhD student Heidi Banse, DVM, Dipl. ACVIM, was one of two inaugural recipients of a $5,000 fellowship to support her endeavors in equine research. The AAEP Foundation and The EQUUS Foundation have partnered to support this fellowship, which seeks to assist equine researchers in exploring horse healthcare topics.

According to the AAEP, Banse's doctoral research, performed under the direction of Dianne McFarlane, DVM, PhD, Dipl. ACVIM, focuses on the molecular events underlying equine metabolic syndrome (EMS). Middle-aged horses are most commonly affected by this endocrine disorder, which results in obesity, regional adiposity, insulin resistance and a predisposition to laminitis. If we can identify the metabolic events that lead to EMS, we may be able to diagnose and treat it earlier, resulting in a better outcome. Banse's long-term goal is to identify an intervention for horses with EMS that is based on better knowledge of endocrine disorder's pathophysiology.

Equine metabolic syndrome: An overview

Photo 1: An obese horse with EMS. (Photos courtesy of Dr. Banse)
Obesity (body condition score of 8 or 9) (Photo 1), regional adiposity (on the neck crest, tail head, prepuce, mammary gland region) (Photo 2) and insulin resistance are all associated with EMS, a condition associated with a predisposition to laminitis (Photo 3). However, the molecular events underlying how laminitis develops in these horses is still not fully understood. EMS most commonly occurs in Morgan horses, Paso Finos, Arabians, Saddlebreds, Quarter horses, Tennessee Walkers and ponies. Most horses with EMS within these breeds are "easy-keepers"—likely to easily put on excessive body weight despite feed restriction.

Photo 2: Regional adipose tissue on a pony’s neck.
Pasture-associated laminitis is common, as access to new rapidly growing spring pasture with a high water-soluble carbohydrate content can allow for high-energy intake and the development of obesity. When horses graze such pasture, increased resting plasma insulin often results.

Photo 3: Laminitis in the same pony as in Photo 2.
In a recent report, Nicholas Frank, DVM, PhD, Department of Large Animal Clinical Sciences, University of Tennessee's College of Veterinary Medicine suggested that for these animals, "hyperinsulinemia is the trigger for disease."1 He also noted, "Pasture grazing also raises the risk of intestinal carbohydrate overload, particularly when animals are moved onto new pastures without gradual transition."

This allows for increased high-energy substrate for the lower gut fermentation, which increases lactic acid concentrations, decreases pH and raises mucosal permeability. This may lead to an increase of various toxins and pro-inflammatory cytokines (tumor necrosis factor alpha, interleukin-1-beta) in the circulation and a potential inflammatory response—in other words, laminitis.