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Background: In metabolically stable horses, alpha‐2‐agonists suppress insulin secretion with transient hyperglycemia and rebound hyperinsulinemia. In horses with insulin dysregulation (ID), the effect of alpha‐2‐agonists has not been investigated; however, both the alpha‐2‐agonist‐induced suppression of insulin secretion and rebound hyperinsulinemia could have clinical relevance. Hypothesis/Objectives: In horses with ID, alpha‐2‐agonists will alter insulin and glucose dynamics. Animals Seven horses with ID and 7 control horses. Methods: In this randomized crossover study, xylazine hydrochloride (1.1 mg/kg) or detomidine hydrochloride (30 μg/kg) were administered IV, and blood was collected for glucose and insulin concentrations at 0, 15, 30, 45, 60, 90, 120, 150, 180, and 300 minutes after administration. Horses received each drug in a random order with a 24‐hour washout period between drugs. Percent change in glucose and insulin concentrations was compared between groups, drugs, and over time with P <.05 considered significant. Results: A significant time‐dependent effect of both alpha‐2‐agonists on glucose and insulin concentrations in control and ID horses was identified (P =.01 for all comparisons). There was no significant effect of sedative selection and endocrine status on blood glucose concentration in either group; however, in ID horses, xylazine administration resulted in severe rebound hyperinsulinemia whereas detomidine administration did not (P =.02). Conclusions and Clinical Importance: Alpha‐2‐agonists have a significant effect on glucose and insulin concentrations in horses. In ID horses, detomidine could minimize hyperinsulinemia when compared to xylazine. [ABSTRACT FROM AUTHOR]