Managing EMS and ID Horses

Researchers continue to hammer home the importance of diet when it comes to preventing serious health problems in horses with equine metabolic syndrome and insulin dysregulation.
Obese horses, possibly suffering from EMS, grazing on grass pasture.
Obesity contributes to equine health problems such as endocrine dysfunction, insulin dysregulation, laminitis, orthopedic disease, infertility, and poor performance. | Getty Images

Worldwide, many horses and ponies are overfed and underexercised—a combination that can easily result in obesity. Some researchers (S Pratt-Phillips 2023) report that about half of horses are overweight and 15-30% are obese. Just as in people, fat deposits and obesity induce important changes to a horse’s metabolic state, leading to hormonal imbalances and insulin dysfunction, which can snowball into laminitis. Because these conditions are so serious, researchers have dedicated significant time and efforts to understanding obesity’s underlying pathophysiology and finding ways to mitigate its adverse effects. With this insight, veterinarians can help educate horse owners on how to achieve preferable body weights in their horses and manage hormonal aberrations in obese animals. 

Consider Metabolic Differences Between Obese and Nonobese Horses 

Obesity contributes to equine health problems such as endocrine dysfunction, insulin dysregulation, laminitis, orthopedic disease, infertility, and poor performance. The term equine metabolic syndrome (EMS) describes a condition often characterized by obesity, insulin dysregulation, and subsequent laminitis. Because gastrointestinal microbiota contribute to the development of metabolic disease, researchers are looking into intricate changes within the microbiome and the metabolome (metabolites of these microorganisms). In a recent study, Coleman et al. aimed to determine if it’s possible to identify horses at risk of obesity by characterizing the fecal microbiota and metabolome and serum lipidome of obese vs. nonobese horses.1  

The study involved two groups of 20 horses from seven farms: 20 obese horses with body condition scores (BCS) ≥ 7 and 20 nonobese controls with BCS of 3-5.  

Previous study results have identified decreased fecal microbial diversity in EMS horses. More sophisticated evaluation techniques are homing in on accurate identification by using whole genome sequencing rather than just focusing on sequencing the 16S ribosomal RNA gene. While Coleman et al. did not find microbiota differences between obese and nonobese horses, they noted differences in the GI metabolome (fecal metabolites) resulting from nutrient ingestion, digestion, and absorption as well as differences in the circulating lipidome.  

The most telling difference relates to intermediates of the mitochondrial tricarboxylic acid (TCA, aka Krebs) cycle that drives anaerobic respiration of cells to produce ATP energy. The study authors said it’s possible that “alterations in energy metabolism of gastrointestinal bacteria contribute to development of persistence of obesity despite appropriate dietary and exercise regimens.” 

Obese horses showed significant increases in circulating free fatty acids compared to control horses. In humans, increased levels of these lipids contribute to insulin resistance and systemic inflammation. The lipid profile of horses resembles that of obese humans. 

Take Home Message for Veterinarians: Alterations in the metabolome and lipidome of obese vs. nonobese horses suggest these two groups of equids metabolize energy differently. This might help explain why some horses do not lose weight despite feeding and exercise programs designed for weight loss. While these researchers did not appreciate differences in fecal microbiota between the two groups, the differences in metabolites were significant. Going forward, these innate differences might help veterinarians better identify horses at risk of developing obesity and implement interventions early, before related sequelae set in. 

9 Dietary Strategies for Managing Hyperinsulinemia 

Strategies for dealing with hyperinsulinemia (HI) and equine metabolic syndrome (EMS) include dietary management, exercise, pharmaceuticals, and corrective farriery. The authors of a recent Australian study stress that dietary modification is a critical component to managing HI in horses with EMS.2 

Insulin-dysregulated horses’ insulin response to oral sugars is a significant predictor of laminitis, referred to as hyperinsulinemia-associated laminitis (HAL). Feeding horses at risk of (or that have developed) laminitis centers on preventing hyperinsulinemia. Horses that are highly insulin dysfunctional have exaggerated insulin responses to most feeds even when consuming “small” amounts of nonstructural carbohydrates (NSC).  

To help prevent HI following feeding, the study authors recommend a number of dietary strategies:  

  1. Eliminate feeds high in NSCs, such as grain, pasture, and cereal hay. 
  1. Implement a weight loss program to minimize biologically active adipokines produced in adipose tissue that play a role in ID development in obese horses. Veterinarians and their clients can accomplish this by: 
  • Restricting energy intake. 
  • Increasing energy output through 30 minutes of moderate exercise three to five times per week, when possible. 
  • Targeting weight loss rates of 0.5-1% body weight each week, tailored to the individual horse. 
  1. The bulk of the diet should be in the form of hay low (< 10%) in water-soluble carbohydrates (WSC) fed at 1.5-2% body weight. It can be divided into small meals and supplemented with a low-calorie ration balancer. 
  • If a horse isn’t responding with weight loss at this amount fed, it is possible to limit forage intake to 1% body weight to more rapidly decrease hyperinsulinemia and body weight by 1% per week.  
  • A study showed that a horse losing 1% of body weight per week did not develop permanent undesirable behaviors or squamous gastric disease. The one issue to watch for with forage restriction is pica and, potentially, sand colic. 
  1. Weigh hay to know exactly how much to offer a horse.  
  1. Soaking hay and pouring off the supernatant also helps decrease the glycemic and insulinemic response by reducing sugar content up to 31%. Some researchers suggest soaking in tap water for 30-60 minutes prior to feeding is sufficient, while others recommend soaking for six to eight hours. Longer soaks might reduce the hay’s dry matter and mineral content in addition to reducing sugars, making it important to provide the horse with a balancer supplement. They give no guarantee, however, that NSC content will reduce below 10% with this strategy. Start with a low-WSC forage that is safe to feed and soak for additional benefit. 
  1. A slow feeder makes hay rations last longer and helps minimize pica and periods of boredom. 
  1. Another strategy for weight loss involves feeding a 50/50 mixture of hay and straw. Monitor for risk of impaction colic from coarse straw. 
  1. Restrict pasture access, since NSC intake exacerbates hyperinsulinemia. 
  • If turning at-risk horses out in pasture, limit turnout to short periods and outfit them with grazing muzzles.  
  • A grazing muzzle reduces grass intake by 30-80%, depending on individual muzzle design and horse adeptness. 
  • Turnout in early morning hours is best because grass sugar content is at its lowest. Bring horses in by mid-morning. 
  • Stress to pasture from frost, herbicides, and poor soil nutrients is known to increase sugars within plants such that even early morning pasture is too rich in sugars. 
  • Use poor grazing areas or strip grazing for turnout. 
  1. Supplement with a prebiotic (such as fructo-oligosaccharides and yeast) that promotes the growth of beneficial gut bacteria to provide a protective effect against insulin resistance and EMS.3  

Lean horses with EMS that do not display the typical obese appearance are the most challenging to feed. The study authors suggest using oils or rice bran for calorie substitution and supplementing with digestible fiber such as beet pulp without molasses. In general, these supplements do not exacerbate hyperinsulinemia yet help the horse maintain body weight. 

Take Home Message for Veterinarians: Dietary management is key to controlling a horse’s insulin response and tendency toward hyperinsulinemia that increases laminitis risk. Weight loss alone does not always resolve insulin dysfunction. The authors of this study recommend measuring insulin pre- and 60-90 minutes post-ingestion to determine the best dietary strategy for minimizing the postprandial insulin response. Each horse likely responds differently to feeding strategies, so tailor the diet accordingly. Sentinel experts are available to help develop customized feeding programs for affected horses at kentfeeds.com/vet-hub. 

References 

  1. Coleman MC, Whitfield-Cargile CM, Madrigal RG, Cohen. Comparison of the microbiome, metabolome, and lipidome of obese and non-obese horses. PLoS ONE 2019, 14(4): e0215918. https://doi.org/10.1371/journal.pone.0215918 
  1. Sundra T, Rossi G, Rendle D, Lestes G. A practical approach to hyperinsulinemia in horses with equine metabolic syndrome.  Equine Veterinary Education 2024; vol 36; pp. 325 – 336; DOI: 10.1111/eve.13938 
  1. Cooke CG, Gibb Z, Grupen CG, et al. Prebiotics and Synbiotics in Equine Health and Disease. International Journal of Equine Science 2023, vol. 2 (2), pp. 37 – 47; https://rasayely-journals.com/index.php/ijes 

This article originally appeared in “Feeding for the Future: Nutrition Knowledge for the Modern Equine Practitioner,” brought to you by Sentinel Horse Feeds. You can download the complete issue here.

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