South African Equine Veterinary Association Congress 2015 Protea Hotel Stellenbosch
concentration is determined to be normal, a dynamic test (usually the oral sugar test) needs to be
performed to document an exaggerated insulin response, supportive of IR. It is also important to
remember that medications can sometimes alter blood glucose and insulin concentrations (i.e., α2-agonists such as xylazine or detomidine). Thus, blood samples should be collected before
sedation that may be needed for farrier work or other diagnostic procedures.
As mentioned, EMS-affected horses do not consistently manifest hyperinsulinemia. In those cases
in which further evidence to support EMS is needed (e.g., for clients that refuse to acknowledge
that their overweight horse may be at risk for laminitis), a dynamic challenge test can be pursued.
Historically, intrave nous administration of glucose (0.1-0.3 g/kg bolus) has been used to
document exaggerated glycemic and insulinemic responses over a 2-4 hour period following
administration. This test documents blunted uptake of glucose by peripheral tissues (a more
profound hyperglycemia) as well as a greater pancreatic insulin response to ultimately return
blood glucose concentration to the normal range. Improved tissue sensitivity to insulin to
management changes, producing weight loss, over time can be documented by performing the test
sequentially. Recently, a more practical test to document IR in suspect EMS horses has been
developed. The test involves an overnight fast followed by oral administration of sugar (75 ml of
Karo syrup light, containing 25 g sugar, to a 500 kg horse) and measurement of insulin
concentration before and 75 minutes after dosing. An exaggerated increase in insulin
concentration (>400 pmol/L [~60 mU/L]) is supportive of IR and EMS. This fairly
straightforward test can also be repeated over time to document improved insulin sensitivity with
weight loss and improved physical conditioning. The oral sugar test also has the advantage of
testing the entire system, including intestinal absorption and tissue uptake of glucose.
Development of a “metabolic profile” that would include physical measurements (e.g., body
weight, body condition score, neck circumference to assess “crestiness”, and others) and
laboratory values (e.g., insulin, glucose, triglycerides, leptin, adiponectin, and others) that would
allow risk assessment for development of laminitis in overweight horses is a goal of several
research groups. Unfortunately, such a profile may take years to develop due to our limited
understanding of EMS pathophysiology. Currently, investigators are also collecting clinical
information and samples for DNA analysis on a large cohort of EMS-affected equids. It is feasible
that genetic markers for increased risk for EMS and laminitis may be an outcome of this study.
Ideally, our goal as veterinarians should be to identify at risk horses prior to onset of laminitis in
order to implement diet changes and an exercise program. Thus, this author strongly advocates
assessment of obesity by performing a body condition score during annual or semi-annual
preventive health care visits. When BCS is 6 or greater, diet should be evaluated (concentrate
feeds discontinued and pasture access limited or a grazing muzzle used) and an exercise program
should be initiated. In addition, hoof conformation should be regularly assessed with an emphasis
on looking for early changes indicative of chronic laminitis. If changes are noted, lateral foot
radiographs should also be pursued. Lastly, a good veterinarian-client relationship is critical for
diet and exercise recommendations to be practically implemented by owners.
Management: Management of EMS can be challenging as it primarily involves client education
and acceptance to comply with dietary recommendations to effect substantial weight loss. In
addition, an understanding of the differences in non-structural carbohydrate content of various
forages is important for appropriate dietary recommendations to be made. Next, implementation
of an exercise program for both at risk and affected horses (those with laminitis) is strongly
recommended for overweight ponies and horses but may difficult to implement in equids
suffering from laminitis. Although medications (thyroid hormone and metformin) and dietary
54