This article has not yet been professionally approved. The information is based on the sources listed below.
EMS in horses: understanding insulin dysregulation and feeding
What equine metabolic syndrome is, why sugar, fructan and starch drive insulin release and how hay, pasture, supplementation and exercise fit together according to the specialist guidelines.
The short answer
EMS describes insulin dysregulation that often goes hand in hand with fat deposits and increases the risk of laminitis 1. The diagnosis is made by your vet practice using suitable tests. For feeding, the guidelines recommend hay with less than 10% NSC, no cereals, no treats, restricted grazing and low-sugar supplementation of minerals, vitamins and protein 2.
What EMS is
Equine metabolic syndrome (EMS) is a cluster of insulin dysregulation, frequently regional or general fat deposits and an increased risk of laminitis 1. The core is insulin dysregulation. Excess weight is often part of it, but it is neither a prerequisite nor proof: there are horses with fat deposits without EMS and horses with EMS without marked excess weight.
Diagnosis belongs at the vet practice. The specialist group recommends dynamic tests in which the insulin response to a defined dose of sugar is measured 2. In horses over ten years of age, it advises testing for PPID (Cushing's disease) at the same time.
Why sugar and starch matter
Non-structural carbohydrates (NSC), i.e. sugar, fructan and starch, are the most important trigger of insulin release 2. In horses with insulin dysregulation, this response is excessive. That is why feeding focuses on where NSC enters the ration: hay, pasture, concentrates and treats.
Insulin levels tend to be higher in winter. The guideline advises avoiding overfeeding and additional NSC-rich feeds during this time 2.
Feeding according to the guidelines
- Hay with less than 10% NSC as the basis, calculated as the sum of water-soluble carbohydrates and starch 2.
- No cereals, no treats and no sugar-rich supplements 2.
- Severely restrict or suspend grazing, depending on the findings and history of laminitis 2.
- Soak unanalysed or NSC-rich hay in cold water for at least 60 minutes 2; longer soaking washes out more minerals 34.
- Balance protein, minerals and vitamins with a low-sugar supplement 21.
Weight loss with support
If the horse is too fat, controlled weight loss is part of the plan. The EMS consensus describes it as a programme with monitoring and individual adjustment, not as a blanket formula for cutting hay 1. The lower limit for forage still applies.
Documenting body condition and weight over time helps you see progress and setbacks 5. Exercise is part of it, but must be tailored individually in the case of laminitis 1.
What supplements can do
For magnesium and chromium, the EMS consensus describes individual indications of improved insulin regulation that other studies have not confirmed 1. A complementary feed replaces neither diagnosis nor a change in feeding.
Basic supply is more important. If the ration becomes tighter or the hay is soaked, protein, minerals and vitamins may be lacking 1. A calculation with your hay values shows which gaps arise.
Key takeaways
- Excess weight is not proof of EMS, and EMS also occurs without marked excess weight 1.
- Sugar, fructan and starch (NSC) are the most important trigger of insulin release 2.
- Hay with less than 10% NSC is the basis; without an analysis, you do not know the value 2.
- A restricted ration needs targeted balancing of protein, minerals and vitamins 1.
Frequently asked questions
How do I recognise EMS in a horse?
Fat pads on the crest of the neck or at the tail head and a history of laminitis can be indications, but they prove nothing 1. Whether insulin dysregulation is present is shown by veterinary tests, such as a dynamic insulin test 2.
Is EMS the same as insulin resistance?
Not quite. The specialist guidelines speak of insulin dysregulation. The term covers an excessive insulin response to feed as well as reduced tissue sensitivity to insulin 1.
Do I need to soak the hay for a horse with EMS?
If the hay has more than 10% NSC or has not been analysed, the guideline states soaking in cold water for at least 60 minutes 2. Minerals are also lost in the process, and the longer the soaking, the more are lost 3. A hay analysis saves you the guesswork.
Can a horse with EMS go out on pasture?
Only to a limited extent and in agreement with your vet practice. A grazing muzzle can reduce grass intake, but its effect varies from horse to horse 67. After laminitis, grazing is only reintroduced once the episode has subsided and on the basis of an insulin test 2.
Sources & studies
The content is based on the references listed below. It does not replace individual veterinary or feeding advice.
Show list of sources (7)
- Durham AE et al. (2019): ECEIM consensus statement on equine metabolic syndrome. Journal of Veterinary Internal Medicine 33:335–349Sections 2–3 and 7: overweight is not an EMS diagnosis; ration adjustment, monitoring and exercise in at-risk horses must be supervised by a vet. Clinical restriction protocols are not adopted as a general recommendation for owners.
- Bertin FR, Bailey S, Burns T, de Laat M, Durham A, Frank N, Kritchevsky J, Menzies-Gow N (Equine Endocrinology Group, 2024): Recommendations for the Diagnosis and Management of Equine Metabolic Syndrome (EMS) and Insulin Dysregulation. Revised June 2024Veterinary expert recommendation, checked on 30 September 2026. Table 1: HAL is by far the most common form of laminitis at over 90%; NSC = water-soluble carbohydrates plus starch, NFC subtraction formulas no longer recommended; NSC as the main trigger of insulin release. Risk factors: NSC-rich ration, age, PPID; overweight aggravating but not consistently. Table 5: hay < 10% NSC; for weight loss 1.5% of body mass as dry matter (1.7% as fed), check every 30 days, lower limit 1.2%; avoid stress because of the risk of hyperlipaemia; straw up to approx. 50% introduced gradually; soak hay in cold water for ≥ 60 min if NSC > 10% or not analysed; hay net/small meals; low-sugar mineral/vitamin/protein balancer; restrict grazing, resume only after laminitis has subsided and an insulin test; pasture NSC varies with temperature, light, rainfall, fertilisation; higher insulin values in winter; exercise only without active laminitis. FAQ: insulin dysregulation in about 30% of PPID horses; test for PPID and ID from 10 years of age. Recommendation for vets, not a guide for owners.
- Martinson K, Jung H, Hathaway M, Sheaffer C (2012): The effect of soaking on protein and mineral loss in Orchardgrass and Alfalfa hay. Journal of Equine Veterinary Science 32(12):776–782Soaking (15–60 min or 12 h) reduces potassium (up to 80%), phosphorus (up to 65%) and magnesium (up to 45%) depending on duration/temperature; effect on crude protein inconsistent/small
- Longland AC, Ince J, Harris PA (2011): Effects of soaking on the water-soluble carbohydrate and crude protein content of hay. Veterinary Record 168(23):618Soaking (up to 16 h, ~8 °C) reduces water-soluble carbohydrates by 27% on average (range 6–54%, fructan ~24%), crude protein remains statistically unchanged
- Henneke DR, Potter GD, Kreider JL, Yeates BF (1983): Relationship between condition score, physical measurements and body fat percentage in mares. Equine Veterinary Journal 15(4):371–372Original publication on the body condition score; bibliographically checked. Its application and limits are additionally supported by horse-specific specialist reviews.
- Longland AC, Barfoot C, Harris PA (2011): The effect of wearing a grazing muzzle vs not wearing a grazing muzzle on pasture dry matter intake by ponies. Journal of Equine Veterinary Science 31(5–6):282–283A grazing muzzle reduced ponies' pasture intake at a sward height of 8–15 cm by around 83%; measured over a few hours, without recording daily intake or weight development
- Glunk EC, Sheaffer CC, Hathaway MR, Martinson KL (2014): Interaction of Grazing Muzzle Use and Grass Species on Forage Intake of Horses. Journal of Equine Veterinary Science 34(7):930–933A grazing muzzle reduced pasture intake at a sward height of 15–20 cm by around 30% on average – markedly less than in Longland et al. (2011). The range between the two studies is too wide for a robust calculation factor