Published February, 2014

In areas or seasons where pasture is unavailable, horse owners turn to hay to make up for their horses' loss of grazing time. But choosing the right hay for a particular horse can present challenges. When feeding hay to horses, many questions arise: What kind, how much, should I buy processed hay, and finally, should I soak the hay for my horse? Soaking hay provides owners with the ability to alter some physical characteristics as well as the nutrient content of their hay if purchasing the ideal hay is not a feasible option.

Why should I soak my hay?

Respirable dust and mold Suboptimal growing and harvesting processes can result in excess dust and/or mold in hay that can cause problems in horses. For example, dust can accumulate in hay grown near dusty roads, and mold can form in hay that has been baled in wet conditions. Dust particles can cause or worsen respiratory problems such as recurrent airway obstruction (RAO). Mold can cause digestive upset such as colic and also produces airborne spores that can cause respiratory diseases in horses. Many studies have shown soaking hay can reduce respirable particle concentration by at least 88%. Soaking can also reduce the amount of mold present.

Nutrient content Some horse owners soak their hay to reduce the amount of sugars, or nonstructural carbohydrates (NSC), in the forage. Horses that require a low-sugar diet, such as those with laminitis or insulin resistance, might benefit from soaked hay. Soaking Orchardgrass hay for an hour, for instance, can reduce NSC by approximately 40%. If the hay started out with 14% NSC, after soaking the concentration would be below the 12% recommended level for feeding horses with laminitis. In addition to removing sugars, soaking also reduces some minerals. Crude protein, calcium, phosphorus, and magnesium concentrations all decrease with soaking. However, certain horses might benefit from the loss of specific nutrients. For example, researchers at the University of California, Davis, School of Veterinary Medicine recommend that horses with hyperkalemic periodic paralysis (HYPP), a metabolic genetic disease, consume a diet containing less than 1.5% of potassium. Soaking Orchardgrass hay for an hour can reduce potassium concentrations from 2.2% to 1.3%. Soaking this hay for 12 hours can bring the potassium concentration down to 0.65%.

How long should I soak my hay?

The length of time you soak your hay results in significant differences in the reduction of respirable particles and nutrients. Soaking hay for 10 minutes can significantly reduce the number of respirable particles in grass hay, and longer soaking times do not necessarily result in a greater reduction in respirable particles. Soaking length does, however, affect sugar concentrations. Generally, the longer alfalfa or cool-season grass hays are soaked, the greater the decrease in these nutrients. In one study, researchers reported that when they soaked cool-season grass hay for an hour, NSC concentrations decreased from 13.8% to 8.6%. When they soaked the same cool-season grass hay for 12 hours, NSC concentrations decreased from 13.8% to 4.8%. Recommendations for hay soaking times range from 30 minutes to an hour to reduce nutrient concentrations for horses with special needs while still being time-efficient.

Will my horse eat soaked hay?

One study has shown that when soaked hay is the only hay offered, there is no difference in a horse's voluntary intake compared to dry hay. Gradually introducing soaked hay into the diet might not only help avoid digestive upset due to a sudden diet change, but might also help a picky eater acclimate to new forage and maintain a normal feed intake.

What are reasons not to soak?

Although soaked hay has many beneficial effects, there are also reasons not to soak. Soaking hay causes a reduction in NSC concentrations, which is the highest energy component of the hay. For horses that have high nutrient requirements, such as performance horses, growing horses, or lactating mares, nutrient losses due to soaking might be a problem. If appropriate hay is already available, such as low-NSC hay for a horse with laminitis, there is no additional benefit of soaking. The soaking process is time-consuming, and soaked hay cannot be stored for extended periods due to the risk of mold. Furthermore, it is difficult to soak in bulk (round bales) for horses in group housing, and soaking hay in cold winter weather is challenging.

Take-Home Message

Veterinarians often recommend soaking hay when feeding horses diagnosed with RAO, HYPP, or laminitis. However, for time and labor’s sake, owners should only soak hay if their ideal forage is not readily available. Hay soaking for short periods of time (30-60 minutes) is an acceptable management method for reducing respirable particles and certain nutrient concentrations. Feed soaked hay immediately after soaking to eliminate the potential for mold growth. Ultimately, owners should rely on forage analysis when choosing a hay that is best suited for their horse and only soak it if they must alter respirable particle or nutrient concentrations.

Ashley Fowler, PhD candidate; Tayler Hansen, MS candidate; Brittany Harlow, PhD candidate; and Laura Strasinger, MS candidate, all in UK’s Department of Animal and Food Sciences, provided this information.