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A look at carbohydrates in hay with the EMS horse in mind

A look at carbohydrates in hay with the EMS horse in mind


Health complications associated with poor nutrition in horses have been documented; the UK National Equine Health Survey (NEHS) 2016 have found that 19% of horses are considered obese using the body condition score. Equine metabolic syndrome (EMS) is a term used to describe several health complications and horses with EMS usually present with obesity, laminitis and insulin resistance.  Although EMS is not fatal, as a result of the significant pain and lameness that results from laminitis, horses are often euthanized.

However, evidence has suggested that with appropriate nutrition intervention EMS and the components that define EMS can be minimised and treated.

In the UK, nutrition strategies put in place to reduce the risk of EMS are to restrict feed intake, reduce access to grass and the practice of soaking hay has become popular in order to reduce the carbohydrate (sugar) content, known to play a part in the development of EMS.

Nutrition Content of Hay

Hay is a vital source of micro-nutrients, proteins and carbohydrates and is therefore a vital part of a horse’s diet. Carbohydrates make up two-thirds of a horse’s diet and are essential for energy as well as providing a source of fibre that is crucial for digestion.  However, carbohydrates are a source of calories and, as with humans, can contribute to obesity if too much are consumed. As a result, monitoring and in some cases reducing the amount of carbohydrate in the horse’s diet can be an effective strategy in treating and reducing the likelihood of a horse/pony being diagnosed with EMS. 

Does Carbohydrate Content Vary in Hay?

There are several factors that influence the carbohydrate content of hay; the type of grass species, the maturity of the hay; mature hay tends to have a lower carbohydrate concentration than younger hay. In addition, weather conditions and time of harvest can also affect the amount of carbohydrate of the hay. Unfortunately, we cannot realistically test each batch of hay we have. Current research is being carried out to formulate a table to help predict the carbohydrate content of different hays in the UK. Experts currently recommend sourcing hay with a carbohydrate content of less than 10% if your horse/pony has been diagnosed with laminitis.

Reducing carbohydrate content in hay

Hay can be treated prior to feeding either by completely submersing the hay in water and soaking it for a period or high temperature steaming using a Haygain, both treatments will reduce the carbohydrate content to some extent. However, due to variable factors including those listed above which affect the carbohydrate starting content these also influence how much carbohydrate is lost. In addition, the length of treatment time and for soaking even the temperature of the water will have an impact.

When you only consider the reduction in carbohydrate content then soaking is generally more effective. However, the drastic increase in bacteria, fungi and yeast over increasing soaking time shown by Wyss and Pradervand (2016) may revoke the benefit.

The current gold standard for reducing carbohydrate content of hay that is above the 10% recommendation uses a combination of soaking and steaming. Moore-Colyer et al 2014 found the most effective method to produce a low-calorie hay which is also clean and safe to feed was to soak for 9 hours and then steam for one hour. Soaking the hay reduces the sugar content, steaming causes further sugar losses but also improves the hygiene quality, getting rid of pathogens that have increased during the soaking process.


Moore-Colyer MJS, Lumbis K, Longland AC, Harris PA. (2014).The effect of five different wetting treatments on the water soluble carbohydrate content and microbial concentration in hay for horses. Plos One

Wyss, U. and Pradervand, N. (2016) Steaming or Soaking. Agroscope Science. Nr 32 p32-33