Is your pony or horse an easy keeper, often over-conditioned and prone to repeated bouts of laminitis? Sounds like insulin resistance or even equine metabolic syndrome might be the culprit, but how can you find out for certain?
“Accurately diagnosing insulin resistance in horses or ponies is an essential first step to correctly feeding and managing them to limit the chances of developing life-threatening laminitis,” explained Kathleen Crandell, PhD, a Kentucky Equine Research nutritionist.
In the development of insulin resistance, horses become less sensitive to the effects of insulin, the hormone secreted by the pancreas that helps control sugar levels in the blood. According to experts in this field*, including Nicholas Frank, DVM, DACVIM, from Tufts Cummings School of Veterinary Medicine, North Grafton, Massachusetts, there are several basic tests to screen for insulin dysregulation, including resting insulin and glucose levels in a blood sample and calculating the ratios of those two values.
“In some horses, these values can be normal even though the horse is actually insulin resistant. In such cases, a dynamic test is needed,” Crandell said.
One such test is the intravenous glucose tolerance test (IVGTT). This test involves taking a blood sample before intravenous administration of sugar (dextrose) and collecting serial blood samples at 1, 15, 30, 45 and 60 minutes after injection. Samples are then analyzed to measure glucose and insulin values.
“In a normal horse, the values of both insulin and sugar increase but then return to normal relatively quickly. In insulin-resistant horses, including those with equine metabolic syndrome, blood sugar and insulin levels increase and remain elevated for a longer period of time,” summarized Crandell.
Although not as simple as taking a single blood sample (the IVGTT involves placing an intravenous catheter and is usually performed in a hospital setting), the IVGTT is far more sensitive and therefore more likely to correctly diagnose horses with insulin resistance. After definitively diagnosing insulin resistance, owner education, diet changes, and an appropriate exercise regime can be instituted to keep these horses as healthy and comfortable as possible.
For more detailed information regarding insulin resistance and equine metabolic syndrome, see Five Reasons to Analyze Horse Forage and Pasture, Insulin Resistance in Horses May Have Hereditary Factor and Managing Horses on High-Fructan Pastures.
*Schuver, A., N. Frank, K.A. Cheroy, et al. 2014. Assessment of insulin and glucose dynamics by using an oral sugar test in horses. Journal of Equine Veterinary Science 34:465-470.
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