Soak Away Your Hay's Hidden Dangers

Soak Away Your Hay's Hidden Dangers

Soaking can help minimize dust and water-soluable carbohydrate levels in hay, which can be harmful for horses that are obese, insulin-resistant, or have metabolic syndrome or respiratory issues.

Photo: Alexandra Beckstett, The Horse Managing Editor

Certain hays and horses don't marry well; here's how to modify your forage

Horse owners are familiar with the refrain repeated by equine veterinarians and nutritionists alike: Feed your horse lots of high-quality hay! Recent studies have extolled the virtues of a forage-only diet for horses—even those with high-energy demands, such as lactating mares. Some scientists say that only the most elite athletic horses truly require dietary supplementation with grains or concentrates to meet their daily energy requirements. So with hay being held in such high regard, how is it that veterinarians and nutritionists dare suggest it’s anything but perfect?

Annette Longland, BSc, PhD, DIC, of Equine Livestock Nutrition Services, in Wales, and Cathy McGowan, BVSc, PhD, DEIM, Dipl. ECEIM, MRCVS, of the University of Liverpool’s Department of Musculoskeletal Biology, Institute of Ageing and Chronic Disease, in the U.K., have both shown that some hays contain so much sugar that they are actually harmful for certain horses to consume. 

In this article we will describe exactly what hay is made of and why anyone in their right mind would want to pay hefty hay prices, only to immediately soak the goodness from every fiber of its being. But be careful—as simple as it sounds, soaking hay can cause major nutrient changes. “Hay soaking should only be considered in horses with diagnosed metabolic diseases and undertaken following advice from your nutritionist or veterinarian,” McGowan says.

What’s Your Hay Made Of?

Many kinds of hay are available throughout the world, based on geographic location, associated growing seasons, and feeding practices/preferences among horse owners in the area. The term “hay” typically refers to either grasses, such as timothy grass, Bermudagrass, and orchardgrass, or legumes, such as alfalfa and red clover. 

Regardless of which hay you choose, they all essentially contain the same basic ingredients: carbohydrates, protein, fat, and water, along with minerals such as calcium, potassium, and phosphorus. The energy (calories) horses derive from hay is primarily from carbohydrates.
 

Hay contains several forms of carbohydrates, all of which are sugar-based molecules. One form is the structural carbohydrate, or fiber, which is predominantly found in the stems rather than the leaves and seeds. Mature hay contains more fiber than younger hay, and it is fermented in the horse’s hindgut (large intestine and colon).

Another form of carbohydrate is the nonstructural or water-soluble carbohydrate (WSC). This type is typically comprised of the simple sugars, such as glucose, fructose, and fructans (which are several fructose sugar molecules joined together). The horse’s body metabolizes glucose and fructose in the small intestine rather than fermenting them in the large intestine. Fructans are fermented in the stomach and small intestine.

Some hays contain substantial amounts of WSCs, occasionally exceeding 250 grams (g) of sugars per kilogram (kg) of dry matter (DM, the resultant hay after it is dried and all the water is removed), Longland says. This is roughly the equivalent of 1.3 cups of granulated sugar in about two pounds of hay. This might not seem like a lot of sugar for your horse’s size and weight, but the current maximum amount of WSCs recommended for horses with insulin resistance (IR) or laminitis is a mere 100 g/kg DM per day.

Soaking can substantially decrease hay’s WSC content, as demonstrated in a paper by Longland published in the January 2014 edition of the Veterinary Record. In her study, four different hays’ WSC content averaged 192 g/kg DM before soaking and 98 g/kg DM after soaking. She says the levels of each individual WSC—fructan, glucose, fructose, and sucrose—decreased following soaking.

That said, some hays still contain considerable amounts of WSCs (>100 g/kg DM) even after soaking. This highlights the importance of having your hay analyzed, especially if feeding a horse or pony with specific dietary needs.

Benefits of Hay Soaking

Many study results have shown that in large enough quantities, WSCs and fructans can harm certain horses. Soaking to minimize hay’s WSC levels, therefore, becomes particularly important for horses that are:

  • Obese; 
  • Insulin resistant; or
  • Diagnosed with equine metabolic syndrome (EMS).

A quick review: After a meal, the horse’s body releases the hormone insulin to control circulating blood sugar levels. Insulin signals cells to store the energy up for body processes later. “In horses with EMS or insulin resistance, large amounts of WSCs are detrimental by causing an excessive insulin response following ingestion,” McGowan says. “This has been called insulin dysregulation and is the key problem in these horses and ponies because we know (prolonged insulin spikes) damage the hoof laminar cells.”

Put simply, this excessive hormone response puts horses at risk for bouts of laminitis (a disease in which the interlocking laminae that support the coffin bone within the hoof fail).

“Initial management for feeding horses with EMS is to restrict access to pasture and to minimize preserved forage (e.g., hay or haylage) to ensure they are not ingesting high levels of WSCs,” McGowan says. “One way to achieve this is by feeding hay that has been soaked.”

She and colleagues demonstrated hay soaking’s benefits in a study published in a 2013 edition of The Veterinary Journal. They soaked hay for eight to 16 hours before offering it to EMS horses at 1.25% of the animals’ body weight, based on DM.

“This study showed that restricting feed intake and offering soaked hay for a carefully monitored six-week period helped horses rapidly lose body mass, improve their body condition score, reduce their belly circumference, and improve their sensitivity to insulin as determined by a test called the combined glucose insulin test,” she says. 

Other horses researchers believe benefit from hay soaking are those with respiratory issues, such as heaves (recurrent airway obstruction). Hay is dusty and moldy, and many scientists have long suspected that soaking hay rather than simply wetting it might better protect horses’ respiratory tracts and improve the stall environment in which they live. But in one study scientists from the University of Edinburgh, in Scotland, showed that simply immersing a filled haynet in water, as well as soaking it for a prolonged period (16 hours), resulted in a decreased “respirable dust concentration” in the horse’s breathing zone—the two-foot sphere around the horse’s nostrils where he draws his breath.  

Soak-by-Soak Instructions 

After soaking your horse's hay for seven to 16 hours, remove it and let the excess soak water drip off, then dispose of the soak liquor away from waterways.

Photo: Alexandra Beckstett, The Horse Managing Editor


After conducting multiple experiments over several years, McGowan, Longland, and colleagues have found that time spent soaking, water temperature, and amount of agitation/stirring during the soak can all impact the degree to which WSCs are removed from the hay. McGowan says these tests have helped her establish some clear do’s and don’ts associated with the art of hay soaking. She suggests trying the following to get started on your quest to absolve hay of its sickly sweet sugars:

  • Fill a clean 64-liter bucket (14 gallons; your average muck bucket holds about 17.5 gallons) with approximately 25 liters (5.5 gallons) of cold water. Water temperature varies throughout the year, which can impact WSC removal. Longland has observed that the warmer the water temperature, the more WSCs will be removed; but once you reach 60°F (16°C), using warmer water won’t make any difference.
     
  • Place a measured amount of hay in a net (about 1.5-2% of your horse’s body weight if fed a hay-only diet, unless other conditions, such as obesity or EMS, dictate feeding more/less).
     
  • Fully submerge the hay in the water. 
     
  • Leave the hay in the water for seven to 16 hours to remove WSCs (or shorter periods for RAO horses), but be aware that warmer water combined with prolonged soaking might also remove important water-soluble minerals. Depending on your goal when soaking, this may or may not be desirable (e.g., leaching of potassium is desirable in horses with hyperkalemic periodic paralysis, but phosphorus removal, which might result in an altered calcium:phosphorus ratio, is not advantageous for any horse). 
     
  • Remove the net, hanging it over the bucket to drain excess soak water before feeding the hay to your horse.
     
  • Once you’ve delivered the soaked hay to your horse, your work is not done. The best way to dispose of the soak liquor, which is an environmental pollutant, is to pour it on grassy areas and rotate the use of those areas. Do not dispose of the liquor in waterways or static ponds.

Several portable commercial soaking systems and steamers are also available to help owners soak hay more efficiently. 

Cautious Soaking 

As simple as it might seem to dunk some hay in a bucket, then offer it to a horse, McGowan emphasizes that owners must carefully approach which horses they offer soaked hay to, and for how long. For example, in the study mentioned above, her team only used hay soaking for horses with early stage EMS. 

“It must be stressed that this is initial management,” she says. “Once I have a horse’s insulin responses back to normal, I put the horses out to pasture.”

In two other studies published in 2014, McGowan and colleagues at the University of Liverpool found that soaked hay contains substantially less energy and dry matter content than fresh hay, which can promote faster weight loss. 

“This means that any restricted intake using soaked hay needs to be carefully monitored to avoid excessive weight loss and secondary problems such as hyperlipemia (excessive mobilization of fat),” she says. “Periods of intense restriction … need to be closely monitored and not continued longer than necessary.”

Take-Home Message

Hay is a nutritious natural food source, capable of providing horses with most (if not all) of their required nutrients. Certain hays and horses do not marry well, however. In those cases hay needs to be modified slightly to decrease the soluble sugars to maximize the hay’s benefits. That said, heed McGowan’s advice and be a responsible soaker! Always discuss dietary modifications with your veterinarian or equine nutritionist before instituting them, and make any changes slowly.

About the Author

Stacey Oke, DVM, MSc

Stacey Oke, MSc, DVM, is a practicing veterinarian and freelance medical writer and editor. She is interested in both large and small animals, as well as complementary and alternative medicine. Since 2005, she's worked as a research consultant for nutritional supplement companies, assisted physicians and veterinarians in publishing research articles and textbooks, and written for a number of educational magazines and websites.

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