Equine Insulin Resistance in the U.S.: What Every Owner Should Know

Insulin resistance (IR) is one of the most common—and most overlooked—metabolic issues in modern horses. Current research estimates that approximately 25% of horses in the United States are insulin resistant (Durham et al., 2019). This means that insulin-sensitive tissues fail to respond normally to circulating insulin, increasing the risk of endocrinopathic laminitis, a painful and potentially devastating condition.

Breeds at Higher Risk

Studies by Frank et al. (2010) and others show that IR is particularly common in:

• Morgans
• Arabians
• Ponies
• Other “thrifty” or easy-keeper breeds

These breeds evolved in nutrient-sparse environments and are genetically predisposed to conserve energy—an advantage in the wild, but a challenge in modern domestic lifestyles where calories are abundant and exercise is limited.

How IR Connects to EMS

The Equine Cushing’s and Insulin Resistance (ECIR) Group and researchers like Johnson et al. (2017) emphasize that IR is a core component of Equine Metabolic Syndrome (EMS). Horses with EMS typically show:

• Regional fat deposits (cresty neck, tailhead)
• Easy weight gain
• High laminitis risk even on small amounts of grass

How IR Is Diagnosed

Veterinarians commonly use:

• Basal insulin blood tests
• The Oral Sugar Test (OST)
• Glucose–insulin dynamic testing

Managing Insulin Resistance

Management focuses on restoring metabolic balance through:

• Diet: low-NSC forage, no added sugars, no grain
• Exercise: consistent, low-impact movement when laminitis is not present
• Supplements: targeted metabolic support as advised by your veterinarian
• Medication: in some cases, veterinarians may prescribe metformin (Rendle et al., 2013)

With one in four horses at risk, early screening, proactive management, and a forage-first, species-appropriate diet remain essential tools for keeping horses healthy and sound.

References

Durham, A.E., et al. (2019). Equine Veterinary Education.
Frank, N., et al. (2010). Journal of Veterinary Internal Medicine.
Johnson, P.J., et al. (2017). Journal of Equine Veterinary Science.
Rendle, D.I., et al. (2013). Equine Veterinary Journal.