To Soak or Not to Soak, That Is the Question ...

Soaking your horse’s hay can be a helpful management strategy (and relatively easy) for owners of horses with certain medical conditions. However, it is important to know the reasoning behind the soaking so that we are not causing any detriment to our four-legged friends.

Conditions that can benefit from hay soaking

Recurrent Airway Obstruction (aka RAO, heaves, or COPD)

RAO is a common respiratory condition of mature horses caused by severe inflammation within the respiratory tract. Similar to human allergies, RAO is managed best with environmental control of allergens such as dust. Researchers have found a decrease in as many as 88% of respirable dust particles after only 30 minutes of hay soaking. This is enough to provide a big improvement for the old “heavey” horse. 

Laminitis, Insulin Resistance, Equine Metabolic Syndrome, PSSM, and Obesity

The conditions listed above are similar in that horses affected by them are quite sensitive to carbohydrate intake, specifically non-structural carbohydrates (NSC or more simply, sugars such as fructans). Soaking grass hay for 15-30 minutes can decrease NSC levels to below 10-12% (the level recommended for these horses). Most alfalfa hay is naturally below the 10-12% level and therefore soaking would not be of any benefit.

HYPP (Hyperkalemic Periodic Paralysis)

Horses affected by HYPP have high levels of potassium within the blood which can lead to muscle twitching and paralysis. Soaking hay can help to leach excess potassium out of the hay. However, soaking to leach out minerals often takes longer (~60 minutes) and when leaching potassium, you will often leach out other important minerals such as calcium or phosphorus. If you are going to soak hay to help manage your horse with HYPP, it is really important to have your hay tested prior to and after soaking to calculate the need for mineral supplementation.   

Rules of thumb for hay soaking

  1. Consult with your veterinarian to know if soaking hay would be beneficial for your horse and to have your hay analyzed to determine if soaking is necessary with your hay type.
  2. Soaking hay for short durations (15-60 minutes maximum) can be helpful for certain equine conditions. Avoid soaking hay for prolonged periods because of the risk of excessive nutrient and mineral loss.
  3. Soaked hay should be fed immediately after soaking to reduce the chance of mold within the hay. 
  4. The temperature of water used has little effect on the amount of nutrients leached or dust reduced during hay soaking.
  5. The liquid remaining after soaking your hay may contain a large amount of phosphorus (can be a pollutant), and the liquid should be disposed of properly (in random grassy areas, not close to water sources).

If you have any questions regarding hay soaking or for a nutritional consultation, don’t hesitate to contact us at Badger Equine Veterinary Services.


Martinson et al. “Hay soaking: all washed up or a good management option?” University of Minnesota Extension,

Hay Soaking” Fact sheet. The Horse:Your Guide to Equine Health Care. Blood Horse Publications. Accessed online: 2013. 

Moore-Coyler, MJ. Effects of soaking hay fodder for horses on dust and mineral content. Journal of Animal Science. 1996;63: 337-42.