Effect of Age and Body Condition on Blood Insulin and Glucose

Obese horses are at higher risk for laminitis, especially during the springtime when pastures are lush, growing quickly, and contain high amounts of sugars. Insulin resistance and elevated blood insulin concentration (hyperinsulinemia) are becoming more recognized and seemingly a more common problem in horses.

A study investigated blood insulin concentration and body condition in 300 mature horses in Virginia. The most common breeds represented were grade, Quarter Horse, Warmblood, and Thoroughbred. Horses ranged in age from 4 to 20 years old. Most horses (58.3%) did not exercise and only 18.3% of horses were in moderate or intense exercise. The majority of horses had continuous access to forage and 84% had continuous access to pasture.

Horses with body condition scores (BCS) equal to or above 7 (on a scale of 1 to 9) had greater blood insulin concentration than horses of BCS 4, 5, or 6.  Obese horses also had higher blood triglyceride (fat) concentrations and lower red blood cell glutathione peroxidase (an antioxidant enzyme). Glutathione peroxidase activity was also lower in older horses. Horses 17 to 20 years of age had higher blood insulin concentration and lower insulin sensitivity than younger horses. Interestingly, hyperinsulinemia and lower insulin sensitivity were not related to BCS in older horses. This may indicate that older horses are at a higher risk of insulin resistance (IR) because of age, independent of body condition. Blood glucose concentrations were also higher in horses of BCS equal to or higher than 7.

This study reported several interesting results. Older horses had indications of IR that were not associated with excessive body condition. Older and obese horses also had decreased activity of glutathione peroxidase, which could predispose them to oxidative stress, which some researchers have also associated with an increased risk for laminitis. This study emphasizes that it is important to feed horses to avoid obesity and maintain optimal body condition. This is especially true for older horses that are at a higher risk for IR with increasing age. Older horses are also more likely to have pituitary pars intermedia dysfunction that can cause IR, hyperinsulinemia, hyperglycemia, and an increased risk of laminitis.

Pleasant, R.S., J.K. Suagee, C.D. Thatcher, F. Elvinger, and R.J. Geor. 2013. Adiposity, plasma insulin, leptin, lipids, and oxidative stress in mature light breed horses. Journal of Veterinary Internal Medicine 27:576-582.