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Thoughts on Soaking Hay for HorsesBy Kentucky Equine Research Staff · December 23, 2014

Some horses can safely eat almost any type of hay. Other horses—those that are overweight or have various metabolic conditions—may get along better on hay with a low nonstructural carbohydrate (NSC) level, thus delivering fewer calories per flake (biscuit) or bale.

Selecting grass rather than legume hay is one way to provide a lower caloric content. Having several types of hay analyzed is another way owners can compare numbers and select forage with less NSC. Finally, soaking hay in cool or warm water will remove a percentage of sugar. This method of calorie control has gained popularity because it is inexpensive and easy to do.

Various figures have been listed as to the amount of sugar that is leached out of hay as it soaks. The reduction in energy depends on the type of hay, its stage of growth, the weather conditions when the hay was cut, cured and baled, and how long it is soaked before being offered to the horse. For the average horse owner, these factors can result in considerable uncertainty as to the effectiveness of soaking in reducing NSC.

According to the results of a trial conducted at the University of Minnesota, 15 to 60 minutes is a reasonable amount of time to allow hay to soak. Longer periods of immersion resulted in very low nonstructural carbohydrate content, a high ratio of calcium to phosphorus, a shortage of phosphorus in the diet, and high dry matter losses.

A recent study carried out in England found that soaking hay for long periods of time (up to nine hours) did reduce NSC levels but also led to proliferation of bacteria, possibly posing a health risk to horses eating the hay. However, steaming this hay for an additional 50 minutes after soaking was effective in decreasing microbial contamination.  

Is there a realistic, time-effective way to get clean, low-NSC hay for horses that will benefit from this type of forage? Kathleen Crandell, Ph.D., an equine nutritionist for Kentucky Equine Research, suggests following these steps:

  • Whenever possible, choose hay that is naturally low in NSC: grass rather than clover or alfalfa (lucerne); made from mature rather than immature forage; cut when plants are grown under average conditions rather than made from plants stressed by environmental conditions like drought.
  • Have hay analyzed for NSC content to see whether it needs to be soaked before feeding. Various grass hays can vary from about 12% to about 20% NSC, and at the high end, these may be too rich for insulin-resistant horses.
  • Hay soaking for short durations (15 to 60 minutes) is an acceptable management method to reduce NSC level in any hay. Longer periods of immersion will remove more NSC but can lead to contamination with bacteria and mold.
  • Remember that all horses need some NSC to provide energy for exercise and body maintenance. Monitor body weights and condition scores on a regular basis and adjust diets as necessary to lose, gain, or maintain an acceptable weight.