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EMS (Equine Metabolic Syndrome) in Horses (2023)

Last updated: 06/2023

Equine metabolic syndrome (EMS) is a collection of risk factors for endocrinopathic laminitis.1 With this type of laminitis accounting for over 90% of laminitis cases, it’s clear that early identification and appropriate management of EMS has an important role to play in safeguarding equine health and welfare.2

What is EMS in horses?

EMS is not a disease in itself, but instead a group of risk factors for endocrinopathic laminitis.  The most important of these risk factors is insulin dysregulation (ID) – a key and consistent finding in these laminitis cases.1 Hyperinsulinemia has been found to be central in the pathogenesis, with research supporting that there is a correlation between the severity of laminitis and the levels of plasma insulin.3

Pituitary pars intermedia dysfunction (View our blog on the health and welfare of horses and ponies with PPID to learn more), formerly equine Cushing’s disease, can also result in ID and is associated with endocrinopathic laminitis. You can find out more about PPID in ‘PPID in Horses (Equine Cushing’s disease)’.

Equine laminitis:

Equine laminitis is a complex, multifactorial and extremely painful condition, affecting up to 34% of horses.4 It occurs when the lamellar structures within the foot change. It can affect any pony or horse and the associated degenerative changes often result in ongoing issues with pain and lameness. You can read more about Laminitis in Horses.

What are the signs of EMS in horses?

Equine metabolic syndrome (EMS) is characterised by obesity, ID (with or without hyperinsulinaemia) and a predisposition to laminitis.1

Other, less consistent features of EMS include:1

  • Predisposition to weight gain
  • Struggle to lose weight 
  • Cardiovascular changes (increased blood pressure, heart rate (HR) and cardiac dimensions)

The main clinical consequence of EMS is laminitis, but obesity may also compromise health and welfare. The signs of laminitis are discussed in Laminitis in horses.

How is EMS in horses diagnosed?

There are several options for assessing ID. Feeding status will affect results, so should be considered when testing. Stress may also cause elevations in insulin in some horses.1

Basal testing1:

Insulin:

Resting (basal) hyperinsulinaemia can be used as an indicator of ID, however, feed intake can affect results, so it is useful to find out what has been eaten and when prior to testing. Fasting prior to testing and feeding cereal-based feeds in the 4-5 hours before testing is not recommended.

Adipokines:

Total adiponectin and high-molecular weight (HMW) adiponectin are both linked with obesity and ID, and low total concentrations can be a risk factor for future episodes of laminitis.

Dynamic testing:

These tests are generally more sensitive than basal testing.

Oral challenge tests:1

Oral glucose test (OGT):

Post-glucose insulin concentrations can be used as an indicator of ID and have been linked with the risk of developing laminitis. To perform the test the animal is usually fasted the night before then fed a meal with 0.5 or 1 g/kg body mass glucose (or dextrose) powder.  Glucose peaks after 60-120 minutes, when a blood sample should be taken.

Oral sugar test (OST):

This uses a specific corn syrup (15-45 ml syrup/100kg body mass), with blood sampling being done 60-90 minutes after dosing to assess insulin response.

Intravenous challenge tests:1

Insulin response test (IRT):

This measures a horse’s glycaemic response to exogenous insulin, directly assessing insulin sensitivity. In horses with insulin resistance (IR), a less than 50% reduction in glucose concentrations is indicative of IR.

Combined glucose insulin test (CGIT):

Glucose, followed by insulin are injected intravenously. Glucose and insulin levels are then assessed after 45 and 75 minutes and compared to basal results. ID is confirmed when there is an exaggerated insulin response and a delayed return to baseline glucose.

Testing for PPID should also be considered in animals with ID and/or laminitis, especially if they are over ten years of age.

Which horses are at risk of EMS?

Some breeds seem to be more predisposed to EMS, including the British native ponies such as Welsh, Dartmoor and Shetland ponies, as well as Arabian and Warmblood horses.5,6 However, any breed can be at risk if their diet and management are unsuitable.1

EMS seems to be more common in less active animals, possibly because exercise benefits insulin regulation as well as playing a role in weight management.1

Sex does not appear to be a factor, but age potentially is, with insulin concentrations generally found to be higher in older animals.1

How does insulin dysregulation occur in EMS?

While the exact cause of ID in EMS is still not fully understood, evidence suggests that the following play a role:1

  • Genetics – an area of ongoing research but several genes have been associated with relevant traits.
  • Epigenetics – foals born to overweight mares have shown ID, low-grade inflammation and an increased risk of developing osteochondrosis.
  • Microbiome – horses with EMS have been shown to have reduced gastrointestinal microbial diversity.
  • Obesity – results in adipose dysregulation affecting the production of adipose-derived hormones (adipokines) which can affect insulin sensitivity.
  • Diet – diets high in non-structural carbohydrate (NSC) reduce insulin sensitivity in horses compared to forage or fat-rich diets.
  • Endocrine-disrupting chemicals – these can be found in commercially produced pesticides and horses living near chemical dump sites in the US have been shown to be at an increased risk of EMS.

Managing horses with EMS

Diet modification and exercise are key to managing horses with EMS but medications to support these husbandry changes can also be beneficial.

Diet:1

Obesity is a frequent feature of EMS and diet restriction to facilitate weight loss is a fundamental aspect of management, helping to improve insulin regulation in these horses and ponies.

  • Total dry matter intake (DMI) should be limited, as should feeds with a high non-structural carbohydrate (NSC) content. For a mixed grass species hay-based diet, 1.25%-1.5% of actual body mass (BM) as DMI is generally recommended.
  • A target weight loss is 0.5-1% BM losses weekly.
  • The nutrient composition of forage should be determined where possible and hays with low NSC content preferred (<10%).
  • Soaking the hay for 7-16 hours is recommended and has been shown to reduce nutrients by 24-43%. In warm conditions soaking for 1-2 hours is indicated to reduce the microbial growth which may be associated with longer soaking times.
  • Access to pasture makes it hard to moderate DMI and grazing pasture with high NSC has been shown to worsen hyperinsulinaemia. Restricting grazing time has little effect on overall intake, although grazing muzzles can be effective. It is recommended that no access to grazing is given during the first 6-12 weeks of dietary restriction.
  • Supplementation with a good quality feed balancer will be required to ensure provision of nutrients.
  • Strategies to slow down ration consumption are beneficial such as double or triple haynets.

Exercise:1

Exercise promotes weight loss and increases insulin sensitivity. However, it needs to be performed regularly at sufficient intensity.

  • Do not exercise horses with current or recent laminitis due to concern over lamellar stability.
  • Increase exercise slowly.
  • In non-laminitic horses with ID – low-to moderate-intensity exercise (canter to fast canter, ridden or unridden, or HRs 130-170 bpm) for >30 minutes, >5 times per week.
  • In recovered laminitic horses, with stable hoof lamellae – low-intensity exercise on a soft surface (fast trot to canter unridden, or HRs 110-150 bpm) for >30 minutes, >3 times per week. Monitor carefully for signs of lameness.

Medications to support EMS management:

There are no authorised medicines for managing EMS but several medications are used, although always alongside diet and exercise modification:

Metformin hydrochloride:

  • A study found that metformin reduced basal insulin concentrations over time.7
  • Oral bioavailability is poor in horses and ponies.8
  • Does not have systemic effects on insulin sensitivity but is thought to have a direct effect on enterocytes to reduce glucose absorption.9, 10

Levothyroxine:

  • Increases metabolic rate to aid weight loss and lowers insulin concentrations through improving insulin sensitivity.5

Sodium glucose co-transport-2 (SGLT2) inhibitors (Ertugliflozin, canagliflozin and velagliflozin):11

  • Are used to treat Type 2 diabetes mellitus in people.
  • Dramatically reduce insulin concentrations in horses with EMS, reduce pain associated with laminitis and are presumed to laminitis risk.
  • Act by inhibiting re-uptake of glucose in the kidney, promoting the excretion of glucose in urine which in turn lowers circulating insulin concentrations.

Ertugliflozin data:12

A study of 51 horses with hyperinsulinaemia and laminitis found there was a statistically significant reduction of median insulin concentrations with oral ertugliflozin. Insulin concentrations were reduced from more than 300u/L to less than 50u/L with an ertugliflozin dose of 0.05mg/kg once daily for 30 days. In addition, a statistically significant reduction in lameness scores was recorded, with most horses showing increased comfort within a few days of starting treatment.

Polyuria and polydipsia were noted in a small proportion of horses and a statistically significant increase in serum triglyceride concentrations. The increase in triglycerides was not associated with clinical signs of hyperlipaemia, and after an initial increase at 30 days, triglyceride levels returned to baseline levels.

See the full paper PPID in Horses (Equine Cushing’s disease).

Pergolide:

We have several webinars on managing obesity and endocrinopathic laminitis:

A heavyweight discussion: how do we tackle equine obesity?

Managing obesity in horses- how can vets help horse owners?

Treatment of equine obesity and laminitis in general practice

Managing endocrine cases through the Autumn and Winter

Abbreviations

EMS – Equine Metabolic Syndrome

References

  1. Durham AE, Frank N, McGowan CM, et al. ECEIM consensus statement on equine metabolic syndrome. J Vet Intern Med. 2019;33(2):335-349. doi:10.1111/jvim.15423
  2. Karikoski NP, Horn I, McGowan TW et al (2011). The prevalence of endocrinopathic laminitis among horses presented for laminitis at a first-opinion/referral equine hospital, Domest Anim Endocrinol 41(3): 111-117.
  3. Walsh DM, McGowan CM, McGowan T et al (2009). Correlation of plasma insulin concentration with laminitis score in a field study of equine Cushing’s disease and equine metabolic syndrome, Journal of Equine Veterinary Science 29(2): 87-94.
  4. Wylie, Claire E et al. “Frequency of equine laminitis: a systematic review with quality appraisal of published evidence.” Veterinary journal (London, England : 1997) vol. 189,3 (2011): 248-56. doi:10.1016/j.tvjl.2011.04.014
  5. Frank, N., Geor, R.J., Bailey, S.R., Durham, A.E. and Johnson, P.J. (2010), Equine Metabolic Syndrome. Journal of Veterinary Internal Medicine, 24: 467-475. https://doi.org/10.1111/j.1939-1676.2010.0503.x
  6. Carslake HB, Pinchbeck GL, McGowan CM. Equine metabolic syndrome in UK native ponies and cobs is highly prevalent with modifiable risk factors. Equine Vet J. 2021;53(5):923-934. doi:10.1111/evj.13378
  7. Durham AE, Rendle DI, Newton JE. The effect of metformin on measurements of insulin sensitivity and beta cell response in 18 horsesand ponies with insulin resistance.Equine Vet J. 2008;40(5):493-500.
  8. Hustace JL, Firshman AM, Mata JE. Pharmacokinetics and bioavail-ability of metformin in horses.Am J Vet Res. 2009;70(5):665-668.
  9. Tinworth KD, Boston RC, Harris PA, Sillence MN, Raidal SL, Noble GK.The effect of oral metformin on insulin sensitivity in insulin-resistantponies.Vet J. 2012;191:79-84.
  10. Bailey CJ, Mynett KJ, Page T. Importance of the intestine as a site ofmetformin-stimulated glucose utilization.Br  J  Pharmacol. 1994;112(2):671-675
  11. https://www.vettimes.co.uk/article/update-on-medical-management-of-equine-endocrine-disorders/
  12. Sundra, T., Kelty, E. & Rendle, D. (2023) Preliminary observations on the use of ertugliflozin in the management of hyperinsulinaemia and laminitis in 51 horses: A case series. Equine Veterinary Education, 35, 311– 320. Available from: https://doi.org/10.1111/eve.13738