Horses with Equine Metabolic Syndrome (EMS) are characterized by insulin resistance, which is hyperinsulinemia (high insulin) with normal blood glucose concentrations.
 

Often, but not always, these horses are overweight with fat pockets at the neck and tail heads.

For more information on body condition scoring and crest scoring, check out the Tribute Equine Nutrition Wellness System.

Horses with EMS have a greater risk of developing laminitis and higher insulin concentrations, which have been associated with more severe changes of the coffin bone. EMS may also be secondary to PPID (Cushing’s Disease), although not all horses with PPID have EMS.

The overall goal in managing horses with metabolic disorders, like EMS or Cushing’s, is to minimize NSC (non-structural carbohydrates) intake while still meeting essential nutrient requirements. Non-structural carbohydrates are comprised of starch and sugar (starch + sugar = NSC). Both must be considered because starch is broken down into sugar before it is absorbed, making the metabolic response the same.

A common pitfall we see with people that own EMS horses is their sole focus on minimizing the percent NSC of a feed without taking feeding rate or NSC of forage into consideration. For example, a single kernel of corn and a bushel of corn are both 75% NSC, though the difference in volume is huge. The metabolic response from consumption of a bushel of corn would be significant, leading to laminitis at the least and likely death. Yet, if a horse with EMS ate a single kernel, it would be just fine.

A horse’s response to NSC intake varies considerably due to a number of factors:

  • Individual variation
  • Amounts (lb) of feedstuff consumed
  • Rate (unit/hour) at which feedstuff is consumed
  • NSC content (%) of feedstuff
  • Feedstuff processing

Figure 1. Variation in individual horse insulin response to NSC intake


CRF E08 MSU27

In Figure 1, two levels of NSC are fed and the blood insulin level was measured for three hours after the meal. With the low NSC treatment (0.66 g/kg intake), most horses maintained fairly steady blood insulin levels; however, horses Bo (blue) and Cav (red) had greater insulin release after the meal. With the high NSC treatment (2.82 g/kg intake), multiple horses showed large spikes in insulin release, yet Fury and Hi maintained fairly steady blood insulin levels. This highlights the individual variation in horse response as well as response to low and high NSC meals.

While many EMS horses are overweight, there is a population of these horses that are unable to maintain enough body condition on forage alone and therefore, require additional calories from a feed or supplement. For harder-keeping EMS horses, feeding a fully fortified feed that provides calories from highly digestible fiber and fat often allows for a lower feeding rate as compared to feeding low NSC ingredients (ex. beet pulp), which aren’t nearly as calorie-dense and thus, require a higher feeding rate.

Figure 2 compares the percent of nutrient requirements met through beet pulp, a low NSC ingredient (8%) that is also low fat (0.5%) and unfortified, to Kalm ‘N EZ® Pelleted, which is fully fortified, moderate fat (8%) and low NSC (13.5%). The higher calorie level of Kalm ‘N EZ® Pelleted allows for a lower feeding rate, which also keeps NSC intake lower (4 lb x 13.5% NSC = 0.54 lb NSC intake) as compared to the beet pulp (7 lb x 8% NSC = 0.56 lb NSC intake), even though the beet pulp has a lower percent NSC.

Figure 2. Percent of nutrient requirements met by hay in combination with 7 lb beet pulp (0.5% fat, 8% NSC) or 4 lb Kalm ‘N EZ® Pelleted (8% fat, 13.5% NSC)

It is also worth noting that the primary source of sugar in the diet of most horses is forage. Growth and harvest conditions greatly influence hay NSC, making it difficult to identify certain varieties of hay that will be “safe”. When feeding a horse that is very sensitive to NSC intake, it is recommended to test hay sources or buy bagged forage with an NSC guarantee. 
 
Dietary management of horses with EMS should focus on minimizing NSC intake, recognizing that forage is the main source of NSC in the diet, while also meeting essential nutrient requirements. For horses that can maintain body condition on forage alone, we recommend feeding Essential K® to meet non-energy nutrient requirements while minimizing NSC intake. Essential K® is a ration balancer and is highly concentrated in essential nutrients while being both low in NSC on a percentage basis and also a low NSC intake product because it is designed to be fed at low volumes (1-2 lb/day). Horses requiring additional calories to maintain body condition can be fed Essential K® with a fat supplement or Kalm ‘N EZ® Pelleted. Kalm ‘N EZ® Pelleted is low NSC (13.5%) while being high in digestible fiber and moderate fat, which allows a lower feeding rate relative to other full intake feeds.
 

Nicole Rambo, Ph.D.