Understanding Sugar in Hay and Non-Structural Carbohydrates (NSC)
Before discussing the effects of steaming, it is important to define 'sugar' in hay. In equine nutrition, this refers to non-structural carbohydrates (NSC), which include simple sugars (ethanol-soluble carbohydrates or ESC) and fructans (water-soluble carbohydrates or WSC), as well as starch. Horses with conditions like Insulin Resistance (IR), Equine Metabolic Syndrome (EMS), and a history of laminitis must have their NSC intake carefully managed. The recommended NSC content for forage for these horses is typically less than 10% on a dry matter basis.
Why Steaming is Not the Most Effective for Sugar Reduction
While steaming is a fantastic way to improve the hygienic quality of hay, its impact on reducing WSC is quite limited. Studies show that high-temperature steaming typically reduces WSC levels by a small and variable amount, ranging from 0-18%. This is not enough for horses requiring a very low-sugar diet. The process uses moist heat to kill mold, bacteria, and dust mites, but it does not effectively leach out the water-soluble sugars from the hay.
The Importance of Respiratory Health
For horses with respiratory conditions like Equine Asthma (Recurrent Airway Obstruction or RAO), steaming is an excellent tool. It reduces the respirable particles (dust, mold spores, bacteria) in the hay by up to 99%, leading to significant improvement in respiratory health. The clean, moist, and more palatable hay also encourages chewing, which can aid digestion.
Steaming vs. Soaking: The Key Differences
For owners needing to reduce the sugar content of hay, comparing steaming and soaking is crucial. Soaking involves submerging the hay in water, which leaches out the water-soluble carbohydrates (WSC). The duration and temperature of the water significantly influence the outcome.
Soaking Hay for Sugar Reduction
- Method: Hay is submerged in clean water for a set period, typically 30 minutes in warm water or 60 minutes in cold water to achieve a moderate reduction. Longer soaking, up to 9-16 hours, can lead to a more significant but variable reduction in WSC (8-50%).
- Pros: More effective at reducing sugar content than steaming, making it a viable option for metabolic horses.
- Cons: Leaches out valuable minerals and nutrients, including protein and vitamins. Prolonged soaking can lead to a rapid increase in bacterial growth, especially in warmer weather, and creates a polluting "hay tea" runoff. The hay can also become less palatable to horses.
Comparison of Hay Treatment Methods
| Feature | Steaming | Soaking | Soaking + Steaming | Dry Hay |
|---|---|---|---|---|
| Sugar Reduction (WSC) | Low (0-18% reduction) | High and variable (8-50% reduction) | High (24-51% reduction reported) | None |
| Microbial Reduction | High (up to 99%) | Increases bacteria count | High (up to 99%) | None |
| Nutrient Loss | Minimal | Significant (minerals and protein) | Significant (minerals and protein) | None |
| Respiratory Health | Excellent, reduces dust and spores | Good (dampens dust) | Excellent, reduces dust and spores | Poor (dust and spores) |
| Palatability | High | Can decrease | Variable | Variable |
| Convenience | Requires special equipment, easier than long soaking | Labor-intensive, messy, and dependent on weather | Most labor-intensive | Easiest |
When is a combination of soaking and steaming necessary?
For horses that require the lowest possible sugar content while maintaining hygienic quality, a combination of prolonged soaking followed by high-temperature steaming is the most effective method. Research suggests that soaking hay for approximately nine hours and then steaming for 50 minutes at high temperatures significantly reduces WSC while killing the bacteria that flourished during the soaking period. However, this is the most labor-intensive approach and still results in the loss of valuable minerals.
The Role of Forage Testing
Regardless of the preparation method, the only way to be certain of your hay's sugar content is to have it professionally tested. Hay testing provides a detailed analysis of NSC levels, allowing you to make informed decisions for horses with specific dietary needs. This practice is especially critical for animals with metabolic disorders, where a high-NSC forage can trigger a laminitic episode. Testing can also help you identify nutrient deficiencies caused by soaking, so you can adjust your horse's supplemental diet accordingly.
Conclusion
In summary, steaming hay does not significantly reduce its sugar content and should not be relied upon as the primary method for this purpose. Its main benefits are for respiratory health and hygiene, not carbohydrate reduction. Soaking is more effective at leaching out sugars, but it comes with drawbacks such as nutrient loss and increased bacterial growth. The best approach depends on your horse's individual health requirements. For horses with severe metabolic issues, sourcing tested low-NSC hay is the gold standard, possibly combined with short-term soaking or a double soak-and-steam process for extreme cases.
Lists of Hay Treatment Best Practices
- Test your hay: Get a professional forage analysis to determine the initial NSC content. This is the only reliable way to know what you are feeding.
- Prioritize hygienic quality with steaming: If your horse has respiratory problems, use high-temperature steaming to reduce dust, mold, and bacteria effectively.
- Reduce sugar with soaking: If you need to lower the sugar content, opt for soaking. Be mindful of nutrient loss and bacterial growth, especially in warm weather.
- Combine methods for specific needs: For horses needing both low-sugar and hygienic hay, consider a prolonged soak followed by a high-temperature steam.
- Supplement for nutrient loss: If you use soaking, remember to provide a balanced vitamin and mineral supplement to compensate for leached nutrients.
- Feed soaked hay promptly: To minimize bacterial growth, feed soaked hay immediately after preparation.
- Manage pasture access: Limit grazing, especially on fresh spring grass or during frosty conditions, as these can be high in sugar.
References
- Soaking or steaming hay - RED MILLS US. Redmillshorse.com. Retrieved October 14, 2025.
- Steaming vs. Soaking Hay for Horses – [Comparison & How-To] - Mad Barn Canada. Madbarn.ca. Retrieved October 14, 2025.
- Hay Steaming – Clean Hay Means Healthier Horses - FSAH UK. Fsah.co.uk. Retrieved October 14, 2025.
- Understanding Sugar and Nonstructural Carbohydrates in Equine Pasture and Hay - OSU Extension Service. Extension.oregonstate.edu. Retrieved October 14, 2025.
