In a recent study applesauce-coated bread slices added about 25% more nonstructural carbohydrates (NSCs) to a group of ponies’ regular diets. While the treats, when fed twice a day, did not impact blood insulin levels, they caused clear changes in how the ponies’ intestines absorbed simple sugars after only 10 days, said Melody de Laat, PhD, BVSc, of the Queensland University of Technology, in Brisbane, Australia.

“Generally, if the horse or pony is meant to be on a low-NSC diet due to equine metabolic syndrome and/or insulin dysregulation, our paper shows that even a small treat can affect their (intestinal hormone communication, or) entero-insular system, and so it might not be an ideal choice,” de Laat said.

Don’t Forget to Count the NSCs in Horse Treats

Insulin-dysregulated horses and ponies release a disproportionate amount of insulin into the bloodstream after meals, especially when the meal includes higher concentrations of NSCs. Grains, concentrated feeds, certain high-sugar forages, and many sweet horse treats are high in NSCs, de Laat said.

To prevent health problems related to insulin dysregulation and obesity, caretakers often calculate and meet the daily nutritional requirements—especially the amount of NSCs—for their at-risk horses and ponies, she said. However, they often don’t include the nutritional content of treats, despite the fact most horse treats—such as apples—contain carbohydrates that could upset that careful balance.

Some veterinarians and nutritionists already recommend limiting such treats for ID horses, de Laat explained.

But researchers still don’t understand to what extent treats might affect ID horses, so her team decided to investigate—all the way down to the intestines.

Insulin and Sugar Absorption in the Small Intestine

The body’s insulin response actually starts in the intestines, specifically, the entero-insular axis between the small intestine and the pancreas, she said. After a meal, certain intestinal factors known as incretins stimulate extra release of insulin. Insulin-dysregulated horses and ponies have higher blood plasma incretin concentrations than metabolically normal animals.

In previous studies, de Laat and her colleagues had found blood plasma levels of the incretin glucagon-like peptide-2 (GLP-2) increased in ID ponies. She explained that GLP-2 in the intestines might be playing an important role in the development of ID by increasing glucose uptake.

A 10-Day Treat Test in 10 Ponies

De Laat and her fellow researchers selected six metabolically healthy and four insulin-dysregulated adult ponies from the Queensland University of Technology research herd. The animals, averaging 13 years old, included five mares and five geldings, including five Shetlands or Shetland crosses, one Welsh pony, one Australian riding pony, one Quarter pony, and two Miniature Horses. The ponies lived in individual housing and consumed a controlled forage diet with an NSC content of 9.9%.

At the start of the experiment, the researchers ran a sugar absorption test using a modified D-xylose sugar to estimate the capacity of the animals’ intestines to absorb simple carbohydrates. They also ran measurements on plasma GLP-2, blood glucose, and serum insulin responses to eating.

They gave each pony one or two—depending on their body weight—slices of whole wheat sandwich bread coated with applesauce twice a day for 10 days. Depending on their individual body weight, the bread and applesauce added between 1.5% and 3.7% NSC content to their daily diets—representing an average increase in NSCs of about 25%. “There were no refusals of the added treat on any occasion,” the team reported.

Afterward the team ran all the same laboratory tests on the ponies again to see how the treat had affected them.

Increased Insulin and Sugar Absorption in the Entero-Insular System After Treats

Following the 10 days of treats, the researchers found that D-xylose absorption in the intestines was 1.6 times higher and that GLP-2 concentrations after meals were 1.4 times higher, de Laat said.

Even so, the daily treats did not seem to affect fasting GLP-2, blood glucose, or serum insulin concentrations, de Laat said.

“The change seen after eating the treat was increased sugar uptake from the intestine—measured by the D-xylose absorption test—and an increase in plasma GLP-2 concentrations in response to feeding,” she explained; in other words, these ponies’ intestinal capacity for absorbing simple carbohydrate increased. “These changes did not go on to affect blood glucose or serum insulin concentrations, before, during, or after eating, however.”

It’s possible that such “early changes” in the entero-insular response after feeding the treats might eventually lead to changes in blood glucose or serum insulin responses if the daily treats continued over a longer period, or if the NSC content of the treat increased, de Laat explained.

However, those hypotheses, as well as the effects of other types of treats, remain to be tested.

The study, “A starch-rich treat affects enteroinsular responses in ponies,” was published in the Journal of the Veterinary Medical Association in December 2022.