Getting Steamed

Here’s the nitty-gritty on soaking and steaming hay

by Kerri-Jo Stewart as published in Jan/Feb 2011 Equine Wellness

Many of us have had to deal with soaking a horse’s hay, whether because of an airway sensitivity or allergy, or for nutritional reasons. And we can relate to the “joys” of handling soaked flakes in sub-zero temperatures (though with new equipment such as the Haydrator, this is getting easier). Now that there are more advanced ways of soaking and steaming hay, it means a greater investment on your part – so does it matter what method you use?

The air they breathe Airborne particulates from hay can negatively affect a horse’s airways, causing respiratory disease and aggravating allergies. To improve air quality, the hay is soaked or steamed so that particulate can't be released into the air while it is still wet. A Clements and Pirie study showed that although wetting the hay decreased airborne particles, there were many other airborne particulates that could negatively affect the respiratory status of stalled horses1. Air quality inside barns is directly related to ventilation and all the materials inside the barn, including bedding. Whatever was in the neighbouring stall was noted as being particularly important. So when searching for the reason your horse is coughing, make sure to look at all the surroundings.

Soak or steam? Soaking hay has long been a popular way to reduce the quantity of dust particles released when horses eat. Now, steaming hay is being touted as a more efficient way to do the same thing. Some research has been done to look at the most beneficial length of time to soak hay in order to get the greatest particulate reduction, as well as the differences between soaking and steaming hay. Clements and Pirie found there wasn't much difference between simply immersing hay in water and soaking it overnight1. A recent study by Kellon also found no differences between soaking times2. Their study also did not find any differences between steaming and soaking the hay. Kellon's trials soaked the hay for ten minutes and 30 minutes, and steamed it for 80 minutes. They found that airborne particulates were reduced by over 90% while the hay remained wet, regardless of the trial. They found that the amount of particulate reduction was the same across all methods of soaking and steaming. Haygain, a steamer manufacturer, states that the primary reason for steaming hay is to control dust and mould spores that cause airway irritation3. They say steamers can eliminate bacteria like salmonella and the pathogens that cause botulism, thus preventing respiratory infections and allergies. Soaking does not completely remove these elements, but it does largely eliminate the possibility of spores being directly inhaled as small airborne particles. Ensuring adequate ventilation, preferably by keeping your horse in an outdoor space, is key to reducing exposure to airborne particulates. If a horse has to be kept indoors, the barn must have excellent ventilation and nothing used inside the barn should produce airborne particulates. But in general, if decreasing airborne particulates is the goal, soaking hay is as effective as steaming.

WSC and the insulin resistant horse The other major reason hay is soaked is to reduce the amount of water soluble carbohydrates (WSC), thereby decreasing the sugar content in the hay. Horses prone to laminitis resulting from insulin resistance and/or obesity should consume feed with less than 10% non-structural carbohydrate, composed of water soluble carbohydrate (WSC) and starch2,3. By soaking hay, the sugar content is leached out with the water and the hay is then believed to be safe for laminitis prone horses. In an older study reported in The Horse, Watts found that soaking can reduce the WSC content by up to 56%4. However, the range in WSC reduction was huge, varying from none to 56%. The researchers analyzed various types of hay, including straight alfalfa, alfalfa-grass mixes, straight grass of several varieties and oat hay, and soaked them for various times in hot and cold water. They found a 10% increase in WCS reduction between soaking the hay for 30 minutes in cold water (average 20% reduction), and 60 minutes in cold and 30 minutes in hot water (average 30% reduction). They also found more correlation between the maturity of the hay than its type when it came to WSC decreases. A 2009 study by the Laminitis Consortium analyzed nine different hay samples for WSC and soaked them for 20 minutes, 40 minutes, three hours and 16 hours5. They found a high variability of WSC in the soaked samples. Although the longer soak did lose more WSCs, very few samples fell below 10% even in the 16-hour soak. The greatest and most consistent loss of WSC was with hay soaked at 16˚C for 16 hours, averaging a loss of just less than 50%. The study’s conclusions were that soaking is an unreliable method for ensuring hay is safe for horses requiring a WSC content of less than 10%. Watts and Ralston found that the average sugar percentage for grass hay ranges from about 6% to 15% but can range anywhere between 3% to 40%3. Given the huge variability in WSC decreases with soaking, it is highly advisable to know both the original quantity of WSC, and the quantity after soaking. A core sample should be taken for analysis following the soaking. This is the only way to know the percentage of WSC in the hay. Kellon's study showed no decrease in WSC content with steaming. To efficiently extract water soluble sugars, large volumes of water are required. Steaming hay is therefore not beneficial for laminitic prone horses.

Nutrient loss Nutrient loss in any food during heating depends on the temperature, duration of heating, and the food type. In general, the longer a food is exposed to heat the greater its nutrient loss6. Current nutritional research typically covers steaming for up to ten minutes. Although testing for nutrient loss in steamed hay hasn't been published, even 30 seconds in steam can alter the nutrient composition of a food and cause some nutrient loss. In general, however, short steaming times are not a practical problem. There is minimal nutrient loss, although temperature and type of food cause large variations in vitamin retention factors. The Laminitis Consortium study also found that greater quantities of protein, vitamins and minerals were lost with longer periods of soaking. Other studies by Haygain have looked at nutrient loss and found that more than ten minutes of soaking leads to considerable mineral loss, particularly sodium, potassium and phosphorus7. Other potential losses include B vitamins, potassium and sodium6.

Palatability and digestibility One touted benefit of steamed hay is that it is more palatable. Haygain states that horses are more likely to eat a poorer quality hay if it has been steamed. However, Kellon's study found that horses did not prefer the steamed hay and required a few days to get used to eating it5. It is not known if steaming hay improves digestibility. A benefit of soaked hay may be performance related. Water soaked feeds increase fluid intake, and soaked hay is easier to chew. Many endurance riders soak their hay during competition for the increased fluid intake.

In conclusion Haygain consultants stated that 80% of horses who are stabled part of the time have some degree of airway inflammation that will affect performance3. Managing a stabled horse involves monitoring all materials in the barn to ensure a low level of airborne particulates, and ensuring the barn has adequate ventilation. Ideally the horse will spend the majority of his time outside. Steaming hay may reduce mould and dust, but it is better to buy good hay without any mould. Horses should not be fed mouldy hay; be aware that adding water to hay may in fact cause mould to form in it. Likewise, if your hay requires steaming in order to kill organisms like salmonella and those that cause botulism, it is better not to use that hay for horse feed. However, of the two methods, steaming will be better at this than soaking, and will yield minimal changes to the hay’s nutrients and sugar components. Since it is extremely important to feed laminitis prone horses a restricted sugar diet that’s less than 10% WSC, the content of WSC in the hay has to be known. Ideally, buy hay that has been tested and has the lowest WSC content. If the hay is over 10% WSC and is being soaked to lower the sugar content, then it needs to be sent for analysis after it's dried to ensure that desired WSC levels are reached. This analysis also gives you the opportunity to balance your horse’s nutrient intake.

Kerri-Jo Stewart has a masters from the University of Guelph in equine physiology and nutrition. She lives with her family in Maple Ridge, BC, with various animals including Akhal-Tekes. She has just published her first photography book, Dreaming in Gold. You can find more about her at Argamak Equine Services.

1. JM Clements, RS Pirie, “Respirable dust concentrations in equine stables,” Res Vet Sci. 2007 Oct;83(2):263-8. Epub 2007 Apr 30
2. Kellon, EM, “Hay Steamers”,, Vol. 17, Number 10, Oct 2010
3. Tietz, N, “Steam-Cooked Hay For Horses”,, May 1, 2010
4. Walcott, K, “Feeding Horses With Laminitis”,, August 01 2004
5. Andrews, M, “Laminitis: value of soaking hay?” , July 7, 2000
6. Wei Sheng, Yan Jiu, “Study on vitamin retention factors in vegetables”, Jan 2008; 37(1):92-6
7. Moore-Colyer 1996, Blackman & Moore-Colyer 1998, “Hay Steamers
8. Haygain Hay Steamers