Unveiling what EMS and ID really look like

Equine metabolic syndrome (EMS) is not a single disease, say members of the Equine Endocrinology Group in their most up-to-date guidelines¹ and authors of the ECEIM consensus statement.² Rather, EMS is a collection of risk factors for endocrinopathic laminitis—the leading cause of laminitis in horses caused by hyperinsulinemia (elevated circulating insulin levels). The most consistent feature of EMS is insulin dysregulation (ID), which veterinarians can measure relatively easily in horses. Another feature they commonly see in EMS cases is increased generalized or regional adiposity—fat deposits all over the horse or in certain spots.

“EMS results from an interaction between genetic and environmental factors, and the risk of laminitis in the individual animal therefore depends on the cumulative effects of these influences,” states the Equine Endocrinology Group in the guidelines.

This means genetically high-risk horses can develop EMS with only minimal environmental (e.g., dietary) influences, whereas other horses that have a lower genetic risk might develop EMS with improper environments, such as diets high in nonstructural carbohydrates (NSCs).

In this article we’ll describe horses and ponies with a higher genetic risk for EMS followed by some examples of other animals with lower genetic risk for EMS that might still benefit from EMS (ID) testing.

“Recognizing EMS in horses other than the ones we expect, the overconditioned equine population, is important because even nonobese and athletic horses are at risk of career- and life-threatening endocrinopathic laminitis if not recognized and treated,” says Teresa Burns, DVM, PhD, Dipl. ACVIM, an associate professor of equine internal medicine at The Ohio State University, in Columbus.

The True Face of EMS: Obese Ponies

The overconditioned population with regional adiposity at the tail head as well as a “cresty” neck is truly the face of EMS, especially ponies. Current estimates suggest 22-27% of ponies are hyperinsulinemic (Durham et al., 2019).¹

“If there ever were a poster child for anything, overconditioned ponies are it for EMS,” says Burns.

“Ponies come by their EMS risk honestly, it seems,” she adds. “But as we are all increasingly aware, there are many other breeds at elevated risk, including—but definitely not limited to—American Saddlebreds, Morgans, Tennessee Walking Horses, Paso Finos, and Arabians.”

We need to look for not only generalized obesity but also regional adiposity.

“Recent work in certain smaller populations failed to identify body condition score more generally as a risk factor for certain components of EMS (like hyperinsulinemia),” Burns explains. “Instead, regional adiposity of the nuchal ligament (in the neck) and tailhead remains predictive.”

For more specific information Burns recommends referring to studies by Fitzgerald et al., 2019³; Barnabé et al., 2023⁴; and Lykkjen et al., 2023.⁵

“It’s also probably not an accident that when EMS-affected animals lose weight, some of the very last adipose tissue to be mobilized is in those high-risk depots,” she adds. “Lean animals often retain these fat depots, especially members of those high-risk breeds. The biological behavior of this fat appears different (more inflammatory, more insulin-resistant) and, in that respect, yes, it may be more important in the setting of monitoring and managing EMS.”

In a recent study a Nigerian research group (Akinniyi et al., 2023) examined the occurrence of EMS in two separate populations of horses: one group of polo ponies residing in Igabi (60 horses) and a second group of companion horses owned by emirates in Zaria (56 horses). In total, 67.8% of the companion horses were diagnosed with EMS, and the prevalence of EMS in obese horses was 92.86%. Obese horses were more than 10 times more likely to have EMS than underconditioned (a body condition score of less than 4.5 on the Henneke 9-point scale) horses, and horses with a cresty neck were nine times more likely have EMS than horses with normal neck crests.⁶

Breeds ‘Resistant’ to Insulin Dysregulation

“Any horse that is overconditioned to the point of obesity can develop EMS, so no breed is completely immune,” says Burns.

Amanda Adams, PhD, an assistant professor at the University of Kentucky Gluck Equine Research Center agrees, adding, “But even a ‘resistant’ breed, if they are pushed with diet/management in the wrong direction, can become EMS/ID.”

Breeds that seem more “resistant” to ID include Thoroughbreds, Standardbreds, and Quarter Horses, Burns says.

“But we have seen members of virtually all breeds within our hospital population affected, including those listed above as well as draft horses,” she adds. “That said, it’s pretty uncommon to see members of those breeds affected if they aren’t first very overweight. They don’t seem to have the same degree of underlying genetic predisposition as do some of the high-risk breeds.”

So, why are certain breeds more resistant, yet not immune to ID and EMS?

“These more resistant breeds more than likely have a genetic factor that is protective, and we have yet to identify the genes responsible for this protective factor,” says Adams.

“Research is ongoing in this area to unravel these questions, but this is not straightforward,” she adds. “And as we know, even if you identify the ‘protective’ or ‘susceptible’ genes of being ID, there is epigenetics in which diet/environment can turn these genes off/on to be over-/underexpressed, which can then influence phenotype (the observable characteristics) of the animal. This is why diet and management are critical regardless of genetic makeup in how we manage our horses to prevent them from becoming ID/EMS.”

Akinniyi et al. also reported that even nonobese horses have ID/EMS. Specifically, nine of the 16 horses (56%) that were underconditioned and 18 out of 61 (29%) horses with a moderate body condition were diagnosed with EMS. The researchers suggested EMS could be related to internal fat or a genetic predisposition. Or, obesity might not be the primary cause and other as-yet-unidentified underlying causes of EMS could exist.

“It’s not a one-size-fits-all category,” says Adams. “There are multiple phenotypes of EMS, including the lean-type EMS horses, which is why diagnostic testing for ID is so important.”

Equine Athletes Can Be Affected by ID/EMS, Too

Even athletic horses can have ID and should not be ignored simply because they compete and are presumptively extremely healthy. Part of this is because many equine athletes are, in fact, overweight. 

As Burns points out, this is particularly true in certain disciplines.

In a study published in a 2023 edition of the Journal of Equine Veterinary Science, Shannon Pratt-Phillips, MSc, PhD, and her group at North Carolina State University, in Raleigh, highlighted the fact that in elite hunter competition, ponies are often overweight or obese by conventional metrics.⁷

“Judges of conformation and appearance appear to reward this,” notices Burns. “Conformation and hunter disciplines seem to favor individuals with higher body condition scores.”

“These findings show that elite competition ponies are dangerously overweight and that adiposity may influence performance in a judged event,” state Pratt-Phillips et al. in the study. “This is of grave concern to the horse industry and needs to be addressed.”

Horses involved in athletic competition, however, do have one advantage over their sedentary counterparts: Exercise has a beneficial effect on insulin regulation. Because certain ponies, such as Shetlands, aren’t exercised as frequently as equids of other breeds, this could play a role in why ponies are at a higher risk of developing EMS/ID.¹

In the Nigerian study Akinniyi reported that 67% of the leisure horses rarely exercised had EMS. However, 20% of the polo ponies that were exercised were still diagnosed with EMS.

Eyeing ‘Healthy’ Horses for Early EMS Signs

While obesity, regional adiposity, and cresty necks certainly tip our radar in the direction of EMS, prompting diagnostics, the at-risk breeds can be affected even while lean and young, says Burns.

Adams notes that “early” signs of EMS/ID are not always easy for people to see, leading owners to believe their horses are healthy.

“Early signs of EMS, such as cresty neck and regional adiposity, including fatty accumulation over the shoulders, ribs, above the eyes, and the rump, can be easily missed by owners if they see the horse daily,” she says. “This is why it’s important to consider ID testing as part of a yearly veterinary examination as a preventative measure.”

This will allow veterinarians to give unbiased evaluation of the animal.

“It’s always better to do the testing rather than guessing,” Adams says.

Horses With Concurrent PPID

If a horse has pituitary pars intermedia dysfunction (PPID, aka equine Cushing’s disease), it’s always a good idea to also test for ID in horses showing clinical signs, says Adams.

Burns adds, “About 30-40% of horses with PPID also have ID.”

But PPID doesn’t necessarily need to be considered in all horses with ID.

“Testing for ID may happen when an animal is on the younger spectrum of age scale, and we know that PPID is more prevalent in older horses,” Adams notes. “I also think testing for both conditions when the horse starts to reach about 15 years of age is a good idea.”

Burns agrees, adding, “As testing strategies for both conditions are refined over time, the prospect of screening populations at risk before any clinical signs of disease are present (and intervening appropriately) is becoming more feasible.”

While researchers are still developing concrete recommendations, Burns says many equine veterinary practices are already adding screening tests to their wellness plans for certain demographics, such as annual measurement of endogenous adrenocorticotropic hormone (ACTH, a hormone that’s elevated in horses with PPID, measured at rest) concentration in the fall for individuals over 15 years of age and annual oral sugar testing in the spring for individuals of breeds predisposed to EMS over 4 or 5 years old.

“Again, such screening protocols for either condition in asymptomatic patients haven’t been validated or formally endorsed, but that capability is a shared goal of several research groups that are active in the field currently,” she adds.

After the Unveiling: Control Hyperinsulinemia

After veterinarians diagnose EMS/ID (see TheHorse.com/1116972), their main treatment goal is to rapidly decrease circulating insulin levels to prevent/quickly resolve laminitis. The Equine Endocrinology Group’s first line of attack on EMS is diet. If you own an animal with EMS, restrict his grazing to little or no grass and stop providing treats and grain (concentrate feed). Here are some other recommendations: Feed to achieve or maintain a body condition score of 5, offering only grass hay low in NSC. (Have the hay tested for NSC content and/or soak the hay to reduce NSCs.) Be certain to offer a low-intake ration balancer with a low sugar content (soaking can leach nutrients from the hay). If laminitis does not preclude exercise, incorporate an exercise program into the horse’s routine. Researchers say even low-intensity exercise involving 30 minutes of unridden fast trot or canter to achieve heart rates of 130-150 beats per minute three times weekly is likely beneficial for these horses.

“It’s important to feed less than 12% NSC hay,” adds Adams. “This is the current guideline; however, my research group is working very hard to put science behind this recommendation. This will better help determine what the ‘safest’ percent NSC in hay is to reduce insulin responses postprandially (after a meal).”

For more information refer to Macon et al., 2022 and 2023.^8-10

Adams also points out that owners not only need to feed low-NSC hay but also restrict the amount of hay they offer to 1.5% of the horse’s body weight per day.

For animals not responding to diet and exercise or in cases of severe laminitis, practitioners might need to rapidly correct ID using medications such as metformin, levothyroxine, and the sodium-glucose cotransporter 2 (SGLT2) inhibitors. These medications are not labeled for horses and must be used under the direct supervision of a veterinarian.

Take-Home Message

Adiposity is a key clinical feature of EMS. Given a preponderance of ponies and horses are overweight, veterinarians and horse owners should consider EMS in many of those animals, particularly if they are at-risk breeds. Still, do not discount EMS in breeds at lower risk, athletic horses, and even other apparently healthy horses. “We should now be actively looking outside of the ‘fluffy’ pony paradigm for equids at risk for EMS,” says Burns. “It can truly affect any of them.”

References:

1. Frank N, Bailey S, Bertin F-R, et al. Recommendations for the diagnosis and management of equine metabolic syndrome. 2022. tinyurl.com/cz2wy8kt

2. Durham AE, Frank N, McGowan CM. ECEIM consensus statement on equine metabolic syndrome. J Vet Intern Med 2019;33(2):335–349.

3. Fitzgerald DM, Anderson ST, Sillence MN, de Laat MA. The cresty neck score is an independent predictor of insulin dysregulation in ponies. PLoS ONE 2019;14(7):e0220203.

4. Barnabé MA, Elliott J, Harris PA, Menzies-Gow NJ. Relationships between total adiponectin concentrations and obesity in native-breed ponies in England. Equine Vet J. 2023. In Press.

5. Lykkjen S, Stenbakk LK, Holmøy IH. Prevalence and risk factors for laminitis within the Norwegian pony breed Nordlandshest/Lyngshest. Acta Vet Scand. 2023;65:22.

6. Akinniyi OO, Sackey AKB, Ochube GE, et al. Occurrence of equine metabolic syndrome, clinical manifestations, and associated risk factors in Nigeria. J Equine Sci 2023;34(2):29–35.

7. Pratt-Phillips S, Munjizun A, Janicki K. Visual assessment of adiposity in elite hunter ponies. J Equine Vet Sci. 2023;121:104199.

8. Macon EL, Harris P, McClendon M, Perron B, Adams A. Insulin dysregulated horses metabolic responses to forage pellets. J Equine Vet Sci. 2023;133:104991.

9. Macon EL, Harris P, Bailey S, Caldwell Barker A, Adams A. Identifying possible thresholds for nonstructural carbohydrates in the insulin dysregulated horse. Equine Vet J. 2023;55(6):1069–1077.

10. Macon EL, Harris P, Bailey S, Barker VD, Adams A. Postprandial insulin responses to various feedstuffs differ in insulin dysregulated horses compared with non-insulin dysregulated controls. Equine Vet J. 2022;54: 574–583.