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Steaming horse hay to reduce the effects of mold and dust

Quick facts

Steaming shouldn’t replace the main goal of feeding hay with low mold and dust content. In the absence of such hay, steaming is a good practice for reducing mold and dust content in moderately moldy hay. You can use steaming to increase forage intake when feeding low mold hay.

Horses are highly sensitive to mold and dust particles from hay and bedding. Breathing in mold or dust can result in respiratory problems. Soaking hay for no more than 60 minutes before feeding can help horses with respiratory problems. Unfortunately, soaking can cause leaching of essential nutrients.

Hay steaming is widely accepted in Europe and is gaining popularity in the United States. We looked at the impact steaming has on forage nutritive value and intake.

Evaluating dust content
We agitated flakes of unsteamed or steamed hay in an electric cement mixer, recorded TSP every minute for 30 minutes.

Testing steamed hay 

We tested steaming on two alfalfa-orchardgrass mixed hays that were low or moderately moldy. We used six adult horses to evaluate preference of steamed and unsteamed hay. We assigned three horses to each hay type (low or moderately moldy) for five days. On day six, we switched the horses to the other hay type.

Each day, we sampled one bale of each hay type for forage quality before and after steaming. We steamed the hay for 90 minutes in a commercial hay steamer. We weighed and offered two flakes of steamed or unsteamed low or moderately moldy hay simultaneously to each horse in individual hay nets.

We allowed the horses 2 hours of access to the hay. We collected the remaining hay and calculated the dry matter intake (DMI). We evaluated the effect of steaming on dust content (TSP) using an additional six bales of both hay types.

Results of hay steaming for 90 minutes


Steaming versus soaking hay

You can use steaming or soaking to reduce how much dust and mold your horse breathes in while eating affected hay. 


Authors: Krishona Martinson, equine Extension specialist, Jim Paulson former Extension dairy educator, Jennifer Earing, former postdoctoral student, Marcia Hathaway, professor emeritus of animal science, Craig Sheaffer, professor of agronomy and plant genetics, Brian Hetchler, research of bioproducts and biosystems engineering, and Larry Jacobson, professor emeritus of bioproducts and biosystems engineering, College of Food, Agriculture and Natural Resource Sciences


Reviewed in 2021

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