Sweeten the Deal: Use Palatable Products for Oral Sugar Test in Horses

A veterinarian-guided oral sugar test (OST) is one way to determine a horse’s insulin status. The test involves ingestion of sugar followed by measurement of blood glucose. Results of this test indicate if horses have insulin dysregulation.

Sounds simple, right? As it turns out, owners can lead horses to sugar, but they can’t make them eat it! Because of this, horses are typically syringe-fed the sugar as a syrup, usually Karo light corn syrup, in a short period of time.

“The necessary volume of Karo light corn syrup ranges from about 225-280 mL (about one cup) for an average-sized horse, which can be challenging to administer without wasting the product,” explained Ashley Fowler, Ph.D., a Kentucky Equine Research nutritionist.

“For comparison, a tube of a standard deworming paste is only about 20 mL. Think about how some horses dislike being dewormed and how much product is wasted or rejected during routine deworming.”

Further, Karo light syrup is not available in all regions of the world, necessitating the use of other sources of sugar. Fowler said that alternative approaches, such as mixing powdered glucose with chaff, are not palatable.

A recent study tested two novel syrups, both similar to Karo light corn syrup but one salty and one apple-flavored, as well as glucose-enriched carbohydrate pellets.^* All three products were fed in amounts that would deliver 0.5 grams of glycemic carbohydrate per kg body weight.

Neither syrup was palatable to any of the 18 horses included in the study when fed in a trough. However, syringe feeding was well accepted with only negligible syrup loss. The novel glycemic pellet was palatable when trough-fed, with 17 of the 18 horses consuming all the pellets within 10 minutes.

All three novel products were compared to an OST performed by delivering a glucose solution directly into the stomach via nasogastric tube, which was considered the reference standard in this study. All horses were fasted for 12 hours before testing.

OSTs were all performed in a herd of Icelandic horses with known insulin status (i.e., sensitive, intermediate, resistant). Results showed that both glucose and insulin responses in the OSTs performed using the two syrups and the novel glycemic pellet all correlated well with the reference standard (i.e., tube-feeding a glucose solution).

“Because the syrups still required a large volume, about 280 mL recommended in this study, the palatable glycemic pellet may prove to be the most efficient way of conducting an OST on the farm,” Fowler said.

Regardless of which approach is ultimately selected, reliable and repeatable testing for insulin dysregulation is necessary to initiate appropriate management.

Current management recommendations for insulin dysregulation focus on diet.

“Horses with insulin dysregulation should be fed diets low in nonstructural carbohydrates (NSC), meaning that owners need to restrict or eliminate pasture access and source hay with less than 10% NSC,” Fowler advised.

Soaking hay is also an option to reduce NSC content, but soaking reduces other key nutrients. Offering a low-sugar ration balancer or vitamin-mineral supplement will help make sure the horse’s nutrient requirements are met.

“For horses with no lameness, exercise can also help improve insulin sensitivity and encourage weight loss in overweight horses,” Fowler said.

These nutritional management strategies are imperative to minimize the development of hyperinsulinemia-associated laminitis (HAL).

“HAL is the most common form of laminitis, resulting from persistently high insulin levels in the horse’s bloodstream. Hyperinsulinemia is a hallmark of equine metabolic syndrome and can also be present in horses with pituitary pars intermedia dysfunction (PPID, equine Cushing’s disease). HAL sometimes becomes a chronic condition in horses that are not nutritionally or medically managed for insulin dysregulation. Over time, the disease can become life-threatening,” explained Fowler.

^*Warnken, T., C. Schaub, and J. Delarocque. 2023. Palatability, glycemic, and insulinemic responses to various carbohydrate formulations: Alternatives for the diagnosis of insulin dysregulation in horses? Journal of Veterinary Internal Medicine 37(1):282-291.