Low Protein Diets for Horses with Equine Metabolic Syndrome

Equine Metabolic Syndrome (EMS) is a collective term that describes horses with an abnormal insulin response after consumption of a meal. This includes Insulin Resistance, as well as several other issues that result in high levels of circulating insulin, which dramatically increases a horse’s risk of developing laminitis. The cornerstone of managing horses with EMS is to limit non-structural carbohydrate (NSC; sugar + starch) intake and maintain a healthy body condition score.

Protein and Equine Metabolic Syndrome

While there is a large body of research that supports the use of low NSC diets for horses with EMS, the impact of protein intake on horses with EMS is a very new area of research. Because some amino acids stimulate the production and release of insulin in other species, there is interest in whether this also occurs in the horse.

Preliminary research (Loos, et al., 2019) does suggest that a meal that is VERY high protein can stimulate greater insulin release in horses with EMS as compared to healthy horses. Understandably, this has led to some confusion and fear about feeding ration balancers to these horses. As with many preliminary research trials, the experimental design doesn’t represent standard management practices in the field (or in this case, the barn).

The main limitation is that the treatment protocol was not representative of how we would normally feed a ration balancer. Over 30 minutes, horses were fed 4 mg/kg bodyweight of a 31% crude protein ration balancer, which is the equivalent of 4 pounds of ration balancer for a 1,000-pound horse. This fulfilled the horse’s entire daily protein requirements in 30 minutes. Under normal feeding guidance, we would typically feed this same size of horse one pound of a ration balancer per day and often split this into two meals. There was also no negative control, meaning that we can’t separate the contribution of protein and the contribution of NSC to the insulin secretion in the EMS horses post meal.

Based on the preliminary study above, Macon and coworkers (2022) compared the insulin response of three ration balancers with low (17%), medium (26%) and high (37%) protein. In this study, the ration balancers were fed at more typical rates (1 pound per meal for a 1,000-pound horse) and the insulin response of horses with and without EMS was compared. Additionally, the amount of NSC was held constant across the three protein levels, which eliminates the question of how much of the insulin response is driven by the protein content versus the NSC content. They found no difference in the insulin response for the different protein levels, suggesting that the protein content, when feeding typical amounts of a ration balancer, isn’t the primary driver of increased insulin production in horses with EMS.

Takeaways from Current Research

As this is an area of research that is in its infancy, there is much to learn about the impact of protein, or even specific amino acids, on horses with EMS. The existing data suggests that the level of protein, when fed at normal feeding rates for a ration balancer, isn’t a primary driver of changes in insulin production in horses. Feeding a ration balancer remains an appropriate approach to provide vitamins, minerals and essential amino acids to horses with Equine Metabolic Syndrome. However, the findings of Loos, et al. 2019 may help explain a relatively common anecdotal experience, which is that some horses with EMS experience greater symptoms when fed a hay that is high in legumes (alfalfa or clover) and, therefore, protein. These symptoms are then diminished or eliminated when these horses are switched to a grass type hay, even though the NSC levels may be comparable or even lower in the legume hay. A focus on not grossly oversupplying protein through the hay is likely warranted based on the current research. Additional research will be required to determine exactly what threshold will be “too high.”

If your horse has been diagnosed with EMS or other NSC sensitivities, our team would love to help you with a personalized feeding plan.


Loos, C. M. M., et al. "A high protein meal affects plasma insulin concentrations and amino acid metabolism in horses with equine metabolic syndrome." The Veterinary Journal 251 (2019): 105341.

Macon, Erica L., et al. "Postprandial insulin responses to various feedstuffs differ in insulin dysregulated horses compared with non‐insulin dysregulated controls." Equine Veterinary Journal 54.3 (2022): 574-583.

Article By: Nicole Rambo, Ph.D.
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