Points to ponder about your horse pastures’ sugars

If you follow veterinarians’ and equine nutritionists’ advice, then the bulk of your horse’s diet is forage, either fresh pasture or hay. Some horses, however, might have health issues, such as insulin dysregulation (ID), that preclude free, ad libitum access to pastures. In this article we will review ID, plant anatomy and sugar content, and learn how to safely manage horses with ID on pasture.

What Is Insulin Dysregulation?

Simply explained, horses with ID produce excess amounts of insulin or respond to insulin abnormally. The pancreas produces insulin and releases it into the bloodstream after the horse consumes meals high in sugars/starch. Insulin prompts the body’s tissues, such as skeletal, muscle, or the liver, to take up glucose from the bloodstream for important metabolic processes such as energy production.

In cases of ID, surplus insulin produced results in high circulating levels of the hormone. This hyperinsulinemia can directly affect tissues of the foot (lamellae), resulting in the extremely painful disease laminitis. Currently, veterinarians report hyperinsulinemia-associated laminitis (HAL) as the leading cause of laminitis in horses.

The most important management strategy for ID, which is the hallmark feature of equine metabolic syndrome (EMS), is reducing horses’ insulin levels. This can be achieved, at least in part, by reducing the amount of sugar in their diets.

“Horses with ID must be closely managed if considering turnout onto pasture. It is not impossible, but careful monitoring of their insulin status and managing turnout to the times of day or days where nonstructural carbohydrate (NSC) content would be at its lowest is critical,” says Carey Williams, PhD, professor in the Department of Animal Sciences and Equine Science Center at Rutgers University, in New Brunswick, New Jersey.  

“Many ID horses might be too severe to have pasture turnout and should have an all-forage diet with NSC containing no more than 10-12%,” she adds.

To truly appreciate why pastures are not suitable for some horses, we need to understand the sugars, fructans, and NSC components of grass plants.

Plant Anatomy

Whereas animals have a musculoskeletal system to support their tissues, plants have cell walls rich in the sugars (carbohydrates) cellulose, hemicellulose, and lignin, which provide the cells strength and rigidity. This explains why nutritionists refer to them as structural carbohydrates. And while cellulose, hemicellulose, and lignin are made of sugar molecules, these molecules are in long chains (polymers) the small intestine cannot digest. Fibers containing structural carbohydrates are instead fermented in the large intestine to produce short-chain fatty acids horses use as their primary energy source