Inflammatory Airway Disease (IAD) is a very common condition in performance horses
First, to eliminate the clinical signs, it is important to know what causes IAD. To date, the exact cause is still not completely isolated. However, what the veterinary community does know is that there is a variety of causative agents that can contribute to the development of IAD. The environmental conditions that horses are exposed to during training, feeding, and housing seem to be the largest pre-disposing factors.
Noninfectious agents are the likely causative factors that create the development of IAD. Horses housed in stables are exposed to high burdens of particulate matter and dust. Within this environment, the horses are also exposed to organic and inorganic particles including fungi, molds, bacteria, mite debris, and other particulate matter.
When managing a horse with IAD, it is important to consider all factors that create exposure to the causative agents. Therefore, the ventilation and bedding must be addressed as well as conditioning of the hay. So, how does steaming hay help a horse with IAD? As discussed above, dust, mold spores, bacteria, etc. are all causative agents of the disease. When hay is steamed, all those causative agents are decreased up to 99 percent (Moore-Colyer et al).
Depending on the severity of the case, a horse may respond clinically to simple environmental management. This would include steaming hay, increasing ventilation in the barn (or more turnout), and low dust bedding. This can be very important for a sport horse that is required to compete under USEF or FEI regulations. Those horses cannot be medicated with bronchodilators and/or steroids during competition. So, it is particularly influential to steam hay for those horses that require being drug free for competition.
Another important point for competition horses that are often traveling is that they have exposure to new inflammatory agents in different environments. So, it is not uncommon for their IAD signs to increase simply due to the stress of travel and exposure to different bacterial, dust, and mold spores that they may encounter in another state or location. This is another strong indicator for a traveling/competition horse to have their hay steamed. Additionally, it is not often practical to bring hay from home if horses are at a competition for a long period of time or traveling overseas. So, the only way to consistently control the airway allergens is to steam their hay ensuring they can compete at their best.
Moore-Colyer, M.J.S. Taylor, J. and James, R (2015). The effect of steaming and soaking on the respirable particle, bacteria, mould and nutrient content in hay for horses. Journal of Equine Veterinary Science. Aug 2015