Hay Soaking: All Washed Up or Good Management?

This article is courtesy of Krishona Martinson, PhD, University of Minnesota.

Soaking hay in water is a common strategy used to manage the nutrition of some diseased horses.  Current hay soaking recommendations include soaking hay for 30 minutes in warm or 60 minutes in cold water for removal of carbohydrates (Watts, 2003).  Soaking hay is commonly done to manage horse diagnosed with laminitis, Polysaccaride Storage Myopathy (PSSM), hyperkalemic periodic paralysis (HYPP), and chronic obstructive pulmonary disease (COPD). 

  • Researchers have suggested that diets contain less than 12 and 10% nonstructural carbohydrates (NSC) for horses affected with laminitis (Frank, 2009) and PSSM (Borgia et al., 2009), respectively. 
  • Reynolds et al. (1997) determined that a diet less than 1% K is necessary for horses diagnosed with HYPP.
  • Moore-Colyer (1996) determined that soaking hay for 30 minutes reduced respiratory problems for horses diagnosed with COPD or heaves. 

However, how efficient is hay soaking, and are additional essential nutrients lost during the soaking process?  Researchers at the University of Minnesota set out to determine the impact of water temperature and soaking duration on removal of NSC, crude protein (CP), minerals, and dry matter (DM) from alfalfa and orchardgrass hays. 

Four hay types were soaked, including bud and flowering alfalfa, and vegetative and flowering orchardgrass.  Individual flakes were submerged for 15, 30 and 60 minutes in 25 liters of cold (72°F) and warm (102°F) water, and for 12 hours in cold water.  A control (non-soaked) sample was also evaluated.  Water temperatures were determined by using the cold or warm only faucets, similar to practices implemented by horse owners and managers.  Subsamples of entire flakes were submitted for nutrient analysis at a commercial laboratory.

  • Prior to soaking, both alfalfa hays were below the 10 and 12% NSC threshold for horses diagnosed with PSSM and laminitis, respectively, and would not have required soaking. The orchardgrass hays were above these thresholds, however, after soaking for 15 to 30 minutes were at or below 10 to 12% NSC. 
    • Although soaking hay for longer durations did further reduce NSC content, it is not recommended.  All horses, even diseased ones, require carbohydrates in their diet. 
    • The severely limited NSC content in hay soaked for greater than 1 hour, combined with increased fiber amounts (fiber components are not water soluble, thus they are concentrated in soaked hay), brings into question the palatability and availability of nutrients in hay soaked for longer periods of time.
  • Crude protein leaching was variable in soaked hays, something other researchers have also observed (Moore-Colyer, 1996).  More importantly, previous research looked at the nutrient availability and quality of rained-on hay fed to steers and suggested the nitrogen remaining in rained-on hay is more stable, water-insoluble (Rotz and Muck, 1994), and possibly less digestible by ruminants (Licitra et al, 1996).  Additional research is needed to evaluate this concept when feeding soaked hay to horses.        
  • Calcium (Ca) is not as prone to leaching during soaking compared to other minerals, and appears to be dependent on hay maturity.  As soaking duration increased, leaching of Ca increased in alfalfa bud and vegetative orchardgrass hays (immature hays).  However, soaking had no effect on Ca leaching in the more mature hays. 
    • Conversely, magnesium (Mg) Mg and phosphorus (P) levels were reduced in all hay types as a result of soaking, with longer soaking durations leading to greater reductions.  Because Ca is not as water soluble as P, high Ca:P ratios were observed in hays soaked for  longer durations, specifically after 12 hours. 
    • Ideally, Ca:P ratios should range from 1:1 to 3:1 (up to 6:1) in horse diets (NRC, 2007).  The high Ca:P ratios observed after longer soaking durations were exaggerated in alfalfa hays which had higher Ca:P ratios prior to soaking. 
    • After 12 hours of soaking, a deficiency in P was observed and ranged from a shortage of 1 to 8 grams for a 500 kg horse in light work (NRC, 2007), and Krook and Maylin [32] suggested that osteochondrosis may be associated with excess dietary Ca. 
  • Soaking both alfalfa and orchardgrass hay for 12 hours was necessary to sufficiently reduce K concentration to recommend levels prior to feeding horses diagnosed with HYPP (Reynolds et al, 1997).  Although K levels can be reduced by soaking, neither alfalfa nor orchardgrass hay is an appropriate option for horses diagnosed with HYPP due to the naturally high levels of K. 

Owners should rely on forage analysis as the primary method of determining the appropriate hay for horses, especially when feeding horses diagnosed with laminitis, PSSM, HYPP or COPD.   Hay soaking for short durations (15 to 30 minutes in duration) is an acceptable management method, but should only be used if ideal hay is not available.  Hay should not soak hay for greater than 1 hour.  Soaking hay for long durations resulted in severely reduced NSC content, high Ca:P ratios, shortage of P in the diet and significant losses in DM.

13 Replies to “Hay Soaking: All Washed Up or Good Management?”

  1. OK, I have a question. When it comes to soaking hay and feeding the hay without the water… I get it. Have there been any studies about soaking hay cubes?
    In my case, I feed soaked hay cubes to my old mare (33 years old) dues to dental issues.

    I soak the cubes for variable amounts of times (real life schedules sometimes makes it difficult to be consistent all of the time). However, when I feed them, I feed the cubes with the water they were soaked in… matching 1 volume of cubes to about 2 times the volume of water. Have there been any studies on this?

    1. Hi Patty, Thanks for the question. Soaking hay cubes is much different than soaking hay. When soaking hay cubes, the goal is to “soften” and allow the cubes to expand. Since you are feeding the cubes with the water (that has been absorbed), the nutrients are essentially “locked in” and we would not expected any leaching of nutrients. We are not aware of any studies on soaking hay cubes, however we wouldn’t anticipate any problems.
      Thanks! Emily L.

  2. I have an 8 year old Arabian gelding that soaks his own hay, it dosen,t matter how far away I put it from the waterer he will drag it over and make hay soup, which also makes a disaster of the waterer, I think he is trying to tell me something, so now when I feed him I put approxmately 3/4 of a gallon of water on his hay and he is happy as a clam.
    I als have a 24 year old arabian mare and she could care less.

  3. My two Arabians were raised on straight grass hay, which we grew on our own farm in Ohio. Since relocating to a ranch in New Mexico, that luxury no longer exists. All my hay is grown in Gunnison, Colorado, and is mixed grass with Timothy, mountain grass, and no alfalfa. Alfalfa seems to be the dominant hay here, as it is just the reverse of the cost in Ohio…here the alfalfa is much less expensive than the grass. Still, paying $16 for a two-strand 85 pound bale, when at one time, it was a whole $1 a bale which covered the cutting and stacking in the barn, makes one be certain they are getting the best hay possible. I shake out the flakes and fluff them up. I then use the hose nozzle on the “gentle rain” setting and wet it down. They both seem to like it just moderately wet. In warm weather, both of them will drag the hay into the water tank for a quick soak on their own!

  4. I have an 5yr old Polish Arabian, he as well soaks his own hay, he get a mouthful and swishes it in his water bucket. This must be a common thing with Arabs? I reacently started spraying his hay to moisten it a little, however he still wets it himself.

  5. I have read your two articles on hay and over the years have determined to feed my horses different diets depending on the season and local climate. Always err on the leaner side of nutrients and increase as the animal requires. I once tried some alfalfa from Canada which was cut in the morning and baled in the afternoon in plastic bags, it was fermented and visible signs of yeast. Smelled like siladge when I opened it and at first, I was not sure whether to feed it. It was a sample bale, sent by producer. I called he said it was supposed to be like that. He said try it, they will love it and it will be good for the digestive system. I tried a small amount first, handful, then gradually increased it. They loved it, went to it before they would their feed. Of course , they did that for alfalfa, orchard, timothy and lespedeza too. When kept upopened and out of the sun, shelf life was 18 months. Know anything about this kind of hay?

    1. Hello Greg, Thanks for the question! Here is the response from Dr. Krishona Martinson from the U of M:

      It is common in Europe and some parts of the U.S to feed “balage” or large square or round-bales that are wrapped individually in plastic. This is commonly done in higher-moisture environments to preserve the quality of the hay. In these environments, hay rarely has that chance to dry to recommend levels (<15% moisture) prior to baling in large bales. If hay is baled too wet (and not wrapped), it will likely mold. Many horses in European countries are maintained on silage or balage, however, there are risks, primarily botulism. The botulism bacterium is a spore-forming, anaerobic bacteria (grows in the absence of oxygen) which is found world wide. It is commonly present in soil and in decaying animal carcasses, and less often in decaying plant material. Hay, especially silage or balage, can be contaminated with the botulism bacterium during the raking and baling process, or if the hay is improperly preserved. Because of this risk, few people feed balage or silage to horses, especially in drier environments where good-quality dried hay is readily available. That being said, if the balage is preserved properly and the horses are acclimated to eating it, its an acceptable hay choice for horses. For more information on this subject, visit http://www.extension.umn.edu/horse/components/pdfs/bale_wrapping_factsheet.pdf.

      Hope this helps.


  6. I have two horses that I soak for using The Soaker from http://www.justsoakit.com. One horse has a history of laminitis and dunking. The other, an iodine deficiency. Since I have been soaking, the one has stopped dunking and his laminitis is gone. The other, all symptoms of iodine deficiency have disappeared. With the soaking, it is much easier for me to add in what they are missing. With the forage analysis I have received, (soak for 1 hour) the soaking has actually put their hay into the normal levels and minimized competing minerals. This article is a great reference. Thanks.

  7. I board my horse and cannot be there to soak hay just prior to it being fed. I’m wondering if I could soak all the day’s hay meals the night before for 15-30 minutes. I’ve read that soaking for more than an hour is not so good. This would mean, though, that after being soaked, the hay meals would be out of water and damp for many hours prior to being fed (10 hrs till breakfast, 14 till lunch, 18 till dinner). So my question is how long after soaking can the hay be fed and still be safe (e.g. not moldy)?

    1. Hello Diana,
      We would not recommend soaking hay the night prior. The speed at which mold can begin to form will vary depending on air temperature, humidity, air circulation wherever it is being stored between soaking and feeding, etc, but the possibility is distinctly there for it to happen. It may not be easy, but we would suggest working out an arrangement with the barn owner/manager for a special service – it will likely be worth the peace of mind.
      Thanks ~ Gina T.

  8. I have an 8 year old AQHA stallion and he is prone to laminitis episodes during vaccines administered in the spring. He also soaks his hay and makes a mess out of his water bucket. Should I just wet his hay when I give it to him? Horses are pretty smart more than we give them credit for. Apparently he has known that he needs to do this for his well being.

    1. Hi Mary, Thanks for the question! If he wants to do it on his own, and as the article suggests it can indeed beneficial to horses to soak their hay if they are prone to laminitis, then we would suggest going ahead and soaking it. Keep in mind that if he is reacting to the vaccines, then it may not be a nutritionally-related laminitis bout and dietary changes may not help. Best of luck! Gayle R.

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