05/26/2026
Equine Insulin
Brian S. Burks, DVM
Diplomate of the American Board of Veterinary Practitioners®
394 Fox Road
Apollo, PA 15613
(724) 727-3481
www.foxrunequine.com
Glucose, the simplest sugar molecule, is the energy currency of the body. Although horses derive free fatty acids from the forage consumed and digested in the colon, there are many cells in the body that require glucose to function, particularly brain and renal cells. Without glucose, these cells cease to function and the organ will die. This molecule requires help getting from the digestive system into the bloodstream and then into various organs and cells.
Insulin is secreted by the pancreas when glucose is ingested, ensuring that it gets into the cells; without insulin and glucose, the cells, and ultimately the body, cannot survive. If the body signals for too much insulin, things can go awry quickly. In some horses, this is a genetic trait, such as Arabians, Morgans, ponies, and some Warmbloods, that causes insulin overproduction.
Horses, like humans, that are insulin resistant continue to overproduce insulin in response to insensitivity, but in humans the pancreas eventually wears out and shuts down insulin production, which is Type 2 diabetes. Unlike humans, horses have a much greater capacity for insulin production, making diabetes rare in horses.
Horses that are overfed carbohydrates can develop laminitis. Insulin activates a cell receptor to allow glucose to enter the cell. There is similar receptor with a different function called insulin-like growth factor (IGF). There is evidence that the lamellar cells in the hoof grow too fast because this cell receptor is accidentally activated and cellular attachment is disrupted, leading to laminitis, a most devastating side effect of insulin dysregulation.
Insulin anomalies do not change equine activity levels, but excessive insulin can damage other organs and can lead to obesity. This may lead to benign fatty tumors/pedunculated limpomas that can twist around the intestine, causing strangulating incarceration and intestinal death, requiring colic surgery. Excessive weight also stresses bones and joints.
Horses with insulin dysregulation are best fed limited carbohydrate diets. Additionally, horses require exercise, medications, and endocrine testing. This typically means avoiding lush green pastures and supplemental concentrates. Severely affected horses should have their hay tested for ethanol soluble carbohydrate (ESC) and starch concentrations, which should not exceed 10% of the daily ration.
Exercise is important to improve insulin sensitivity in both horses and humans. Daily lunging or riding at a trot or canter is required, not just turn out to wander in the pasture. They need to break a sweat. Of course, horses with laminitis may not be able to exercise due to compromise of the feet.
Horses that cannot exercise often benefit from synthetic thyroxine to speed up metabolism and reduce development of fat deposits. It also improves insulin sensitivity.
Older horses are at risk for diseases such as pituitary pars intermedia dysfunction (PPID, or equine Cushing’s disease). Age and body condition will affect insulin concentrations, so an annual test would be wise in a previously diagnosed case.
Radiographs of the feet can also be quite helpful. Laminitis can be quite insidious and the horse might not be overtly lame, but radiographic changes can be significant.
