Cover Story | Nutrition

Feeding Strategies for the Insulin-Dysregulated Horse

By Paul Basilio

Endocrinopathic laminitis is the most common form of clinical laminitis, and horses with insulin dysregulation (ID) are at a significantly higher risk for developing the potentially debilitating disease. While medical treatment has its place in the management of some horses, the most effective way to manage and prevent episodes of endocrinopathic laminitis is through precise nutrition.

In a healthy horse, resting insulin levels are typically less than 20 IU. When horses with ID are fed a grain meal that produces postprandial hyperinsulinemia, they start to approach the proposed laminitic insulin threshold of around 200 to 300 IU.

“In practice, the threshold is different for each horse,” said Erica L. Macon, MS, PAS, PhD, during a presentation at the 70th AAEP Annual Convention in Orlando. “We want to try to limit postprandial hyperinsulinemia because we don’t yet understand how often insulin needs to be elevated” to raise the risk for endocrinopathic laminitis.

Current Research
Dr. Macon described a study in which she and her colleagues found that horses with ID had a reduced postprandial insulin response when fed a lower non-structural (NSC) feed (6% NSC), which led them to speculate that ID horses have a threshold for NSC from feeds.

During a follow-up study, they painstakingly developed diets with varying starch and sugar, also known as nonstructural carbohydrate (NSC), levels to identify that threshold. The feeds varied from 5.1% to 17.13% NSC (0.05 g/kg body weight [BW] to 0.19 g/kg BW), and they were fed at a rate of 1 g/kg of body weight.

The ID horses had higher insulin responses to all feedstuffs vs. healthy horses, as expected.

“We did learn a few things,” said Dr. Macon, who is an assistant professor of equine science at Texas A&M University. “For example, ID horses have a lower threshold for starch when compared with sugar. That makes sense, since the horse actually doesn’t produce a great amount of amylase.”

This result also makes sense in the context of the horse’s natural diet, which is mainly forage. The starch percentage of those diets is typically 1% to 2% at most.

The researchers also identified the threshold for total NSC at 0.1 g/kg BW—17 times lower than the threshold for healthy horses. “The caveat is that we used pure sources of sugar and starch, not something in a completely feed matrix,” she added. “The threshold might be slightly higher if it was included in a feed matrix.”

She described another study in which ponies with ID were fed either soaked hay (10.9% NSC), dry hay (16.0% NSC), or haylage (18.5% NSC). Results showed that once the NSC concentration was above 10% to 11%, the ponies began to have marked insulin responses, according to a study in The Veterinary Journal.

Implementing Nutrition Strategies
Dr. Macon recommended veterinarians should calculate the NSC of a particular feed for ID horses or ponies to determine just how much NSC the animal is getting with each feeding. If the NSC concentrations are above the 0.1 g/kg BW threshold, the feed can be split over multiple meals to avoid large fluctuations in postprandial insulin levels.

Nutrient content can vary from lot to lot of a specific feed. Owners can request lot-specific nutrient analyses from most manufacturers. In addition, Dr. Macon pointed out that not every low-NSC feed is actually low in NSC.

“You have to make sure that you go through and calculate the NSC regardless of what your client decides to feed their horse,” she explained. “Make sure you’re not going to exaggerate that postprandial response.”

Even if a feed has a higher than advertised NSC concentration or exceeds the 0.1 g/kg BW threshold, there are still options, such as splitting a meal into thirds to spread out the insulin response.

“Low-NSC feeds are not all equal,” she said. “They need to be calculated for each individual horse, and nutrition strategies should be implemented wherever possible.”

Mechanical methods, such as slow-feeder buckets or grazing muzzles, can decrease feeding time and potentially blunt the postprandial insulin fluctuations.

“We need to have more research conducted in this area to see if that actually lowers insulin responses,” Dr. Macon cautioned. MeV

For more information:
Macon EL, Harris P, Bailey S, et al. Identifying possible thresholds for nonstructural carbohydrates in the insulin dysregulated horse.
Equine Vet J. 2023;55(6):1069-1077. https://pubmed.ncbi.nlm.nih.gov/36537847/

Carslake HB, Argo CM, Pinchbeck GL, et al. Insulinaemic and glycaemic responses to three forages in ponies. Vet J. 2018;235:83-89.
https://pubmed.ncbi.nlm.nih.gov/29704944/