Why do We Steam Hay?

It is unfortunately very common for horses and ponies to develop a cough when stabled for long periods. It is thought that this is due to a mixture of issues – bedding, forage, ventilation, stable hygiene as well as genetics to name a few. Even though there may not be any visible signs of dust, bacteria or mould in hay, research has shown that they are present in all hays and can be a respiratory irritant. As you would expect, hay which has been properly dried and stored has lower levels of dust, bacteria and mould when compared to hay that has been baled slightly damp (as is often done in sunny England!).

Traditionally you would soak hay if your horse developed a cough, however, over recent years it has become more widely known that this practice can increase the bacterial content up to 5-fold if soaked for 9 hours. Even 10 minutes soaking has been shown to increase bacterial load by 1.5-fold!

How do Hay Organisms Affect horses?

Breathing - What is Heaves?

Recurrent airway obstruction, also known as broken wind, heaves, wind-broke horse, or sometimes by the term usually reserved for humans, chronic obstructive pulmonary disease (COPD) – it is a respiratory disease or chronic condition of horses involving an allergic bronchitis characterised by wheezing, coughing and laboured breathing.

Caused by an allergic reaction to certain otherwise innocuous substances - allergens, typically dust and mold spores (e.g. Aspergillus spp.). It is therefore most common in horses fed on hay and bedded on straw. Endotoxins from organisms in the bedding and feedstuffs may also play a role.

Brain - Bacteria & Mycotoxins
Gut - Nematodes and Parasites

What happens when you wet or steam Hay?


Soaking hay or wetting hay with a kettle is easy to do, helps to reduce dust and so can ease a cough. Neither method will do anything to reduce moulds and spores in the hay, which may continue to affect the horse.

Strong wetting, especially soaking, has been proven to massively increase bacterial loads in the hay. This will typically push bacteria counts into the do-not-eat zone.


Adding a lot of hot water or steaming unevenly creates zones where Bacteria can thrive. Bacteria are activated above around 20 degrees Celsius and thrive up to 40-50 degrees after which they remain active, but slow down their multiplication. 


Steaming Hay above 55 degrees Celsius kills most parasitic Nematodes and will slow bacterial and mould activity so their breeding effectively stops. It will not reduce populations, however.


Steaming Hay above 65 degrees Celsius will kill most Moulds, Penicillium & Aspergillus species as well as Ascomyceten, Algaes, Insects, Worms, Snails and some viruses.

75 - 90°C

Steaming above 75 degrees Celsius effectively kills plant pathogenic bacteria and all Penicillium and Aspergillus species.

Closer to 90 degrees Celsius mesophilic moulds are killed off and many bacteria, but spores remain.


Steaming above 90 degrees Celsius is effective in killing spore-forming bacteria and their spores along with all mould spores. research has shown that 10 minutes above 90 degrees Celsius is required to reduce bacterial loads by up to 98%.

The Equisteam has been independently Lab-tested to show it reliably steams in this range across the hay load.

So how does a EquiSteam Hay Steamer help?

Helps reduce or eliminate Heaves

By eliminating dust, spores and other irritants, your horses' allergic reactions are greatly reduced or even eliminated. Combined with a clean stable environment Steaming has been proven effective in reducing or eliminating Heaves.

Kills Moulds and spore-forming bacteria

By heating the Hay up to a level that kills bacteria and mould spores as well as all other lesser nasties, you get Hay that is clean and fit for feeding.

By concentrating the Steam in a smaller chamber we can ensure the hay is steamed evenly, with no cool zones to shelter bacteria and allow them to multiply.

Horses prefer the hay and are cleaner with it

Steaming (even after Soaking) improves the palatability of hay to the point that Horses have been proven to prefer it.

The result is a happier horse, more of the hay eaten and less hay scattered in the stable and walked into your bedding.

Convenient Soaking and Steaming

Where soaking is required (typically for dietary requirements), the EquiSteam can be filled with water to pre-soak a Haynet.

It can then be easily drained and then steamed to kill off the bacteria and other organisms that multiplied during the soaking process.

Easy to move and clean

An EquiSteam Hay Steamer is lighter and much easier to move and drain than most other designs. A deep drainage channel in the base keeps Hay out of the bacterial soup produced by condensing water soaking through the Hay.

Steam chambers can be easily relocated and stacked for storage.

Flexible steaming with 1 or 2 chambers

With the choice of 1, 2 or more Steam Chambers, one steam-generator can be used across one, or multiple units.

Our dual-connection hose adapter allows rapid steaming of one or two Chambers at a time. With robust quick-release fittings, the unit can be used sequentially with as many Chambers as you can fit into the day.

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