Steaming hay for the Insulin Resistant horse – May be as good or better than soaking

By Juliet M. Getty, Ph.D.

You have no choice. Soaking seems to be the only option for your hay. It’s too high in non-structural carbohydrates (NSC) and your insulin resistant horse is at risk of developing laminitis.

There is considerable research on soaking[i] and it can be a worthwhile option. Soaking removes sugars and fructans, known as water soluble carbohydrates (WSC), as well as some starch (WSC + Starch = NSC). The warmer the water temperature and the longer you soak it, the more you remove. This makes inherent sense and researchers at the University of Minnesota have confirmed that NSC levels decline significantly when hay is soaked in warm water for 30 minutes or cold water for 60 minutes. But there are real disadvantages.

Soaking causes considerable mineral losses. It also reduces the amount of dry matter, leaving your horse with less digestible fiber. Bacterial growth is a problem if hay is soaked for more than two hours. On top of all that, it is just plain difficult! Wet hay is heavy. Soaking is nearly impossible in winter. And hay floats - you have to weigh it down to immerse it in water. Draining all that water can be messy. The hay starts to mildew very quickly if not immediately eaten. And, some horses simply do not like it. Need I go on?

Steaming reduces NSC

Typically done to control dust and mold spores for horses with respiratory problems, steaming is also an effective means of reducing NSC. Horses suffering from insulin resistance due to obesity, metabolic syndrome, or equine Cushing’s disease, as well as from insulin sensitivity due to polysaccharide storage myopathy (PSSM), need to be fed grass hay, free-choice, that has an acceptable NSC level of less than 12% (and ideally, below 10%) on an as-sampled basis. Some researchers suggest that steaming does not remove as much NSC as soaking[ii], but the amount removed can vary. Here is the result of a recent study:[iii]

While it is apparent from the above table that soaking does a better job of reducing NSC, the hay used in this study started out with a high NSC level (20.8%). Notice that neither approach reduced the NSC to an acceptable level. Therefore, it is advisable to first test your hay, and then retest after treatment. If your hay starts with a more moderate NSC level, say 13% on a dry matter basis, steaming may bring it down to a level that is safe for your horse. Furthermore, it is worthwhile to look at the “as-sampled” basis instead of the “dry matter” basis because the hay that your horse consumes when dry has some moisture in it (typically around 10%). Therefore, the “as-sampled” numbers are a better indicator of how much sugar and starch your horse is actually eating. Consider the example below using the 7.2% NSC reduction rate produced by steaming as shown in table 1:

The above numbers demonstrate that steaming will reduce the NSC to 12.06% on a 100% dry matter basis. But even better, the NSC level is actually brought down to 10.86% on an as-sampled basis -- safe to feed for most insulin resistant horses. Furthermore, it is safe to feed free-choice to your overweight horse to allow for self-regulation and ultimate weight loss.

Even more favorable results have been revealed.

If your hay has a high NSC percentage, don’t despair. Follow the manufacturer instructions for length of steaming time and retest your hay after steaming. Take a look at this study’s results[iv] where the WSC dramatically improved:

While starch measurements were not included in the above study, it revealed a far more dramatic decrease in WSC (18.3%) than the results shown in table 1 (with less than 3% WSC reduction).

Mineral status is maintained

Copper, zinc, manganese, magnesium, calcium, and phosphorus were not lost by steaming. In fact, since steaming opens up the fiber matrix of hay, the bioavailability of these minerals is likely enhanced

Bottom line

Steaming makes hay more palatable, it is much easier to perform, and depending on your hay, can significantly improve the WSC level to a point where it is safe to feed free-choice to your horse. Always test your hay before and after treatment.


The above article offers insight into the benefits of steaming on reducing non-structural carbohydrates (NSC). For more details on hay, NSC, and the needs of the insulin resistant, cushingoid, or PSSM horse, please refer to Feed Your Horse Like A Horse

[i] Martinson, K.L., Hathaway, M., Jung, H., and Schaeffer, C. from the University of Minnesota. 2011 through 2012. Several studies on the effect of soaking on protein, mineral, carbohydrates, and dry matter losses.

[ii] Kellon, E. 2010. Hay steamers. Horse-Journal, 17(10). October.

[iii] Adapted from Kentucky Equine Research, June 16, 2012. The effect of soaking or steaming timothy hay on voluntary intake and digestibility by Thoroughbreds. Timothy hay was soaked at room temperature for 30 minutes, or steamed in a HAYGAIN steamer and allow to reach a temperature of 170 degrees F

[iv] Moore-Colyer, M. 2009. A summary of an investigation into the nutrient content of hay steamed for 50 minutes in the Haygain steamer. Royal Agricultural College, Cirencester, Glos.