Horse owners who use heated barns to keep water from freezing and to protect horses from cold temperatures during winter should remember supplemental heat can cause problems if used incorrectly.

Ventilation is important when horses are kept inside a barn, said Dave Freeman, Oklahoma State University Cooperative Extension equine specialist.

“Closing up a barn to maintain heat may increase respiratory diseases because of high ammonia content and bacterial growth in stalls,” Freeman said.

Closed barns usually have increased humidity. High humidity combined with warm temperature can cause enough nitrogen smell or bacteria growth to irritate the horse’s respiratory system. These frequently result in chronic, minor respiratory problems that interfere with animal performance.

Freeman said controlled research to define acceptable humidity and temperature levels to lessen the chance of respiratory illnesses is difficult because of the variability between barns, the horse’s daily routines in and out of the barn and lack of controlling research conditions. However, many veterinarians attest to an increase in respiratory problems in heated barns with high humidity.