The air in many livestock buildings contains noxious mixtures of microorganisms such as molds, bacteria, viruses, plant materials, dust particles, feces, and gases. Many high-quality sport horses spend 23 hours per day in their stalls, so the quality of air in their stables is an important factor in maintaining their heath. A horse's respiratory tract is susceptible to these noxious gases, and the most common mistake made when constructing horse barns is failing to provide adequate ventilation. The gas most commonly identified in stables is ammonia, which can damage the respiratory tract of humans and animals, and can increase the chance of infections. Sulfur dioxide is also in horse stables and has a noxious influence on health and of animals and people. The carbon sulfide can cause the trachea to become inflamed. Also, you have to be concerned with carbon monoxide and other gases emanating from internal combustion engines if these are used in or near the horse stable. Just cranking a tractor in the same barn will increase the amount of noxious gases in a barn that has insufficient ventilation.
To study the amount of noxious gases in a horse stable, a group of veterinarians in Poland studied the issue and the results, published in the JVES, indicated that natural gases were highest in the morning hours after the horses had been in all night, and they decreased after leaving a gate open during the day. Also, these noxious stable gases can lead to can lead to asthma in humans, chronic obstructive pulmonary disease in humans and horses, and recurrent airway obstruction or heaves in horses So the more you can keep your horses out of the barn and the more open you can keep your barn to increase airflow the better for your horses.