In the equine industry, few conditions are as concerning and frustrating as insulin dysregulation (ID). Insulin dysregulation is a complex endocrine disorder affecting a large percentage of the equine population and is the defining characteristic of equine metabolic syndrome (EMS). Most critically, ID increases the risk of laminitis, a painful and potentially career- or life-ending condition.  

Current management strategies focus on restricting pasture access and feeding low nonstructural carbohydrate (NSC) rations. While widely recommended, these approaches have historically relied on limited scientific validation, particularly regarding how ID horses respond to pasture and long-stem forages of varying NSC concentrations, and restrictive grazing strategies. Morgan Askins’ doctoral research at the University of Kentucky seeks to fill these knowledge gaps by generating data driven recommendations that help veterinarians and horse owners proactively manage this devastating condition.  

Understanding the Impact of Pasture and Seasonality  

Seasonal fluctuations in pasture NSC concentrations pose a continual challenge for managing ID horses. To better understand this relationship, insulin concentrations were monitored in ID and non–insulin dysregulated (NID) horses for two 24-hour grazing periods in late summer and spring. Elevated pasture NSC levels were associated with significantly increased insulin concentrations in ID horses. Importantly, when ID horses were removed from pasture and housed on a drylot with low NSC hay, insulin concentrations decreased rapidly and remained reduced within 24 hours. These findings highlight both the metabolic sensitivity of ID horses to pasture carbohydrates and the effectiveness of rapid dietary intervention.  

Long-Stem Forages and the Insulin Response  

Researchers on a five-week randomized crossover study evaluated the insulin response to six long-stem forages with varying NSC concentrations in both ID and NID horses. Although two of the forages contained <10% DM NSC, they still produced an augmented insulin response compared to a negative control (low NSC pellet). Results suggest that feeding more than 0.13-0.135 g NSC/kg body weight per meal may result in an exaggerated insulin response in ID horses. These findings emphasize that total NSC intake per meal, not only percentage NSC on a forage analysis must be considered when developing feeding strategies for ID horses. 

Restrictive Grazing Strategies: Evidence for Practical Tools  

To better understand real-world management practices, a nationwide survey assessed the use of restrictive grazing methods in the U.S. A total of 91% of respondents reported utilizing at least one restrictive grazing strategy, most commonly grazing muzzles or dry lots, to prevent or manage laminitis or excessive weight gain. Grazing muzzles were most frequently used for nine to 12 hours per day during spring and summer.  

To evaluate the effectiveness of grazing muzzles, nine ID horses were monitored during four, 10- hour summer grazing periods using a replicated 2×2 crossover design. Horses grazing with a muzzle demonstrated significantly lower insulin concentrations compared to unmuzzled controls, under low-moderate pasture NSC (6.0-13.8% DM) conditions. This data provides scientific validation for a commonly used management tool.  

Advancing Proactive Management of Insulin Dysregulation  

Collectively, this body of work highlights the critical influence of seasonality, pasture NSC content, forage intake, and grazing management strategies on insulin dynamics in ID horses. The findings support the use of dry lots with low NSC hay and grazing muzzles as potentially effective tools to reduce the insulinemic response in ID horses.  

However, ongoing monitoring remains essential. NSC concentrations can fluctuate rapidly with environmental conditions, and individual metabolic responses vary. By refining feeding recommendations through controlled research, these studies aims to improve equine metabolic health, reduce laminitis risk and provide veterinarians and horse owners with practical, scientifically validated tools for managing ID horses.  

This is an excerpt from Equine Disease Quarterly, Vol. 35, Issue 2, funded by underwriters at Lloyd’s, London, brokers, and their Kentucky agents. It was written by Morgan Askins, MS, PhD candidate, at the University of Kentucky’s Gluck Equine Research Center, in Lexington.