It is just a fact of life that all baled hay develops some amount of mold. In well put up hay, hay that is suitable for horses, the amount is undetectable by inspection. However, if hay is bailed before it is adequately dry or becomes wet during storage, molds flourish producing large numbers of spores. Chronic exposure to large amounts of mold spores causes a serious allergic condition in horses called Heaves, chronic obstructive pulmonary disease (COPD), and more recently has been referred to as recurrent obstructive airway disease (ROAD). This article discusses the detection of moldy hay and what to do about it. We have an article on Diagnosing and Treating Heaves.

Molded hay when severe is easy to spot, you can see the mold as areas of white mold and black rotted hay, that smell musty to foul. This is obviously not acceptable, not only is heaves a concern but toxins in the mold and rotted areas represent health threats to your horse. However it is not the mold you see on the hay that causes heaves.

Hay that was just a little too moist may not form mold you can see on the hay but it does form large numbers of spores. These spores appear as dust in a newly opened bale and when inhaled over a period of time the horse will develop an allergy to the spores, that causes an allergic bronchopneumonia. Initially the horse has a cough when first exercised but with continued exposure and develop difficult breathing...more.

Detecting Mold Spores in Hay

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