This article has not yet been professionally approved. The information is based on the sources listed below.
Steaming hay: when a hay steamer makes sense
Steaming mainly reduces dust, microbes and fungal spores; soaking mainly reduces sugar. What the studies show about both methods and which one suits which goal.
The short answer
A hay steamer mainly improves hygiene: in one study, microbial and fungal load fell markedly, while sugar, protein and mineral contents did not decrease significantly 1. If you want to lower the sugar content, you have to soak; this reduces water-soluble carbohydrates by around a quarter on average, with a wide range 2. Which method fits therefore depends on the goal.
What steaming does
In a comparative study with five treatments, steaming did not significantly change the contents of sugar, nitrogen and minerals such as sodium, calcium, magnesium, phosphorus and potassium. The effect was essentially hygienic: fewer microbes and fungi 1.
What soaking does
Soaking for up to 16 hours lowered water-soluble carbohydrates by 27% on average, with a range of 6 to 54%; crude protein remained unchanged 2. With longer soaking, however, phosphorus, potassium and magnesium are also lost 3. The microbial load can increase as a result of soaking 1.
Which method for which goal?
| Goal | Steaming | Soaking |
|---|---|---|
| Less dust, microbes, spores | Yes | Dust yes, microbes rather more |
| Less sugar | Hardly | Yes, with a wide range |
| Retain minerals | Yes | Losses with duration |
Summary of the cited studies; not a recommendation for any particular device.
Clarify hay quality first
Neither steaming nor soaking makes spoiled hay good. A sensory assessment of smell, colour, structure and contamination gives a first impression; hay with mould should not be fed 4. Microbiological quality can be tested in the laboratory using the VDLUFA method 5.
If your horse is coughing or showing breathing problems, the cause should be clarified by a vet. Steamed hay can then be part of the management, but it does not replace treatment.
Key takeaways
Frequently asked questions
Does steaming reduce the sugar content of hay?
Hardly. In the comparative study, sugar, nitrogen and minerals did not change significantly as a result of steaming 1. Soaking is the appropriate method for lowering sugar 2.
Is steamed hay better than soaked hay?
For hygiene, yes: soaking can even increase the microbial load, whereas steaming reduces it 1. For sugar, no. If you need both, it is best to discuss the combination with your vet practice.
Can I steam mouldy hay and feed it?
No. Hay with mould should not be fed, based on the sensory assessment 4. Steaming is a hygiene measure for sound hay, not a rescue for spoiled hay.
Sources & studies
The content is based on the references listed below. It does not replace individual veterinary or feeding advice.
Show list of sources (5)
- Moore-Colyer MJS, Lumbis K, Longland A, Harris P (2014): The Effect of Five Different Wetting Treatments on the Nutrient Content and Microbial Concentration in Hay for Horses. PLOS ONE 9(11):e114079Steaming does not significantly change sugar, nitrogen and mineral contents (incl. Na, Ca, Mg, P, K) – the effect is essentially hygienic (dust, microbes)
- Longland AC, Ince J, Harris PA (2011): Effects of soaking on the water-soluble carbohydrate and crude protein content of hay. Veterinary Record 168(23):618Soaking (up to 16 h, ~8 °C) reduces water-soluble carbohydrates by 27% on average (range 6–54%, fructan ~24%), crude protein remains statistically unchanged
- Martinson K, Jung H, Hathaway M, Sheaffer C (2012): The effect of soaking on protein and mineral loss in Orchardgrass and Alfalfa hay. Journal of Equine Veterinary Science 32(12):776–782Soaking (15–60 min or 12 h) reduces potassium (up to 80%), phosphorus (up to 65%) and magnesium (up to 45%) depending on duration/temperature; effect on crude protein inconsistent/small
- Bayerische Landesanstalt für Landwirtschaft (LfL): Gruber Tabelle zur PferdefütterungPractical reference table with requirement and feed values based on the GfE recommendations; the basis of many ration calculations in German-speaking countries. Chapter 9.3, Table 39: most common poisonous plants for horses with habitat, toxicity and risk level (after Kamphues et al. 2014)
- VDLUFA – Methodenbuch III (Futtermittel)Reference methods of agricultural testing laboratories (LUFA) for the analysis of feeds and forages