Insulin Dysregulation in Nonobese, Nontraditional Breeds of Horses

The classic picture of equine metabolic syndrome (EMS) is that of an obese pony, Arabian, Saddlebred, or any “easy keeper” with chronic laminitis, usually standing in a field of lush grass. The problem with this picture is that it does not truly convey how dangerous EMS is or the devastating effects this syndrome has on equine health. More importantly, this picture doesn’t highlight the fact that even nonobese horses can have EMS.^*

Insulin dysregulation is a central feature of EMS, defined as a combination of high fasting or postprandial (fed) levels of insulin. Veterinarians most commonly use the oral sugar test (OST) for diagnosing ID, with insulin levels >45m μIU/mL 60 minutes after administering Karo light corn syrup (0.15 mL/kg). Nonlaboratory methods of “screening” horses and ponies for insulin dysregulation, and therefore EMS, include obesity and morphometric measurements, such as cresty neck score.

Due to the dearth of information on insulin dysregulation in nonobese stock-type breeds such as Quarter Horses, Paints, and Appaloosas, veterinary researchers recently performed an OST and cresty neck score in 62 stock-type horses owned by Mississippi State University or its clients. Neck measurements were taken when the horses were standing relaxed. Measurements included neck length and neck circumference at 25%, 50%, and 75% along the neck length, as well as crest height.

“Insulin dysregulation was diagnosed in three horses, which was about 5% of the study population. This shows that, while uncommon, insulin dysregulation does occur in nonobese (<7/9 BCS) horses of these breeds,” explained Catherine Whitehouse, M.S., a Kentucky Equine Research nutritionist.

No important relationships between insulin levels and neck measurements were observed.

Whithouse added, “These data also show that obesity and neck measurements should not solely be used to assess horses for insulin dysregulation.”

Some experts suggest that insulin dysregulation testing (such as an oral sugar test) should be conducted as part of a horse’s annual physical examination.

“Early identification of insulin dysregulation allows us to effectively manage these horses, helping reduce the risk of laminitis. Older horses and those not in regular work may have a greater chance of developing metabolic disorders. Therefore, these horses may benefit from proactive veterinary monitoring to detect changes in glucose and insulin metabolism,” Whitehouse relayed.

Once diagnosed, management centers around dietary modifications.

According to Whitehouse, feeding programs should focus on supplying adequate calories to support an ideal weight and body condition score.

“A general rule of thumb is to maintain horses at a body condition score of 4.5-6 on the Henneke nine-point scoring system. For most horses with insulin dysregulation, this may translate to a ration of moderate-quality forage with a vitamin and mineral supplement or ration balancer. For nonobese ID horses that may need to gain weight, calories can be supplied by low-starch and low-sugar feedstuffs, including high-calorie forages, fat supplements such as vegetable oil, and specialty fortified feeds,” Whitehouse explained.

EO-3, a marine-derived oil rich in the long-chain polyunsaturated fatty acids EPA and DHA, is research proven to increase glucose tolerance and insulin sensitivity.

 ^*Heaton, C.P., C.A. Cavinder, E.N. McClure, T. Smith, W.B. Smith, N. Liburt, A. Krotky, and P. Harris. 2024. Prevalence of insulin dysregulation in the non-obese stock-type horse and relationship with morphometric neck measurements. Journal of Equine Veterinary Science 141:105151.