Insulin Dysregulation
Beginning with a brief refresher, Erica Macon, MS, PAS, PhD, Assistant Professor of Equine Science in the Department of Animal Science at Texas A&M University’s College of Agriculture and Life Sciences, defined insulin dysregulation (ID) as “a collective term for tissue insulin resistance and either resting and/or postprandial hyperinsulinemia.”
Any horse independent of age, sex, and breed can have ID. While many practitioners and owners think ID primarily affects horses with generalized obesity, regional fat, and chronic laminitis/laminitic hoof rings, Macon said, “Any horse can develop ID, and often the worst cases are those that you would least expect (i.e., thin phenotype).”
Veterinarians diagnose ID through resting insulin levels or, preferably, insulin levels following an oral sugar test (OST).
“These horses should be maintained on a diet low in nonstructural carbohydrates and kept off grain before the test,” Macon said. “For horses, use 0.15 mL/kg body weight Karo syrup, but use 0.45 mL/kg in ponies or borderline cases. If the insulin level is greater than 45 uIU/mL 60 minutes after syrup administration, then the horse is diagnosed with ID.”
Pituitary Pars Intermedia Dysfunction
Moving on to pituitary pars intermedia dysfunction (PPID), Macon said this endocrinopathy is typically considered a geriatric horse disease, occurring independent of breed. Females are more commonly affected than males, and the most common clinical sign is hypertrichosis/coat changes and muscle atrophy.
“Before testing horses for PPID, do not offer grain five to six hours beforehand, and ensure they are not stressed/running around. Wait 30 minutes if they were stressed at all,” advised Macon.
Veterinarians can diagnose the condition with the resting ACTH or the TRH stimulation tests. Macon recommended using the Equine Endocrinology Groups’ recommendations, especially when taking season into consideration.
Horses can, of course, have the “double whammy,” with both ID and PPID.
“These horses are normally over 15 years old, have regional adiposity; however, we’re also seeing lean PPID/ID horses,” Macon warned.
Related Reading
- Managing EMS and ID Horses
- Impact of Transportation on ID Testing in Horses
- Implications of Imprecise Sampling Times for TRH Testing
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