Equine Metabolic Syndrome and Equine Cushing’s Disease

or is on pasture. Fasting blood samples are a holdover from carnivores and humans horses are tricklefeeders and fasting samples can and do give falsely negative results. There may be a small increase in insulin for two to four hours after the very first haygrass meal of the day if the horse has had no hay overnight so schedule the blood pull four hours or more after the first meal of the day in that situation.
This is a good time to mention laboratory reference ranges. A horse can have an insulin that appears to fall within the laboratory reference range and hence is normal but these reference ranges cover a wide range of circumstances. While an insulin of 30 uIUmL may be appropriate for a horse that has had a grain meal in the last couple of hours it is a clear indicator of an abnormal insulin response in a horse that has been eating only lowstarch and lowsugar hay. The best way to evaluate the insulin and glucose results is to plug them into the IR Calculator which can be found on the ECIR website www ecirhorse org under the Insulin Resistance menu. This calculator was developed from the groundbreaking work at the Virginia Polytechnic Institute by Treiber Kronfeld Hess et al in the mid2000s. Their exhaustive work on the Institutes research herd allowed them to develop calculations that would predict which animals were at risk of laminitis and hence were considered EMS.
The gold standard for diagnosing EMS in a research setting is to use an oral sugar test as well as the intravenous glucose andor insulin challenge. In practice it is more desirable to use a single blood pull to check for insulin glucose and leptin for two reasons. First and most important if the horse already has high circulating levels of insulin the addition of extra glucose to the system and the subsequent insulin spike can cause further damage to the hooves. The second reason is that the multiple blood samples two or more used in these tests adds expense. If a horse has all the appearances of EMS but is still showing as nonIR in the IR calculator then the oral sugar test may be appropriate. If the horse has an abnormally high basal insulin then there is no need to proceed to the oral sugar test or an intravenous challenge test.