Two experiments were conducted to evaluate the effect of feeding endophyte-infected fescue seed on insulin regulation in equids. Experiment 1 examined the impact of endophyte-infected (E+), endophyte-free (E-), and novel endophyte (NE) infected tall fescue seed on metabolically normal horses. Treatment type did not significantly affect resting or post oral sugar test (OST) insulin and glucose concentrations. No treatment effect on body weight, lameness scores, or hoof sensitivity was observed between treatments, though body weight decreased significantly during the feeding period in all treatment groups. Experiment 2 examined the impact of E+ and E- tall fescue seed on insulin-dysregulated (ID) ponies. Treatment type did not significantly affect resting or post OST insulin and glucose concentrations, but ponies showed an increase in peak insulin concentrations at the end of the treatment period compared to baseline, regardless of treatment type. No treatment effect on body weight or lameness was observed in ID ponies. Future research is warranted to investigate these differences and further characterize the overall effect of toxic endophytes on metabolic function horses and ponies.