No single cause of IAD has been identified, although there has been plentiful speculation about the role of environment, viral disease, bacterial infection, air pollution, and genetic predisposition. Although horses with IAD do not seem to experience bouts of overt airway obstruction on exposure to an allergenic environment, organic dust associated with stabling likely contributes to the initial inflammation. Sweeney noted that the racehorses in her study lived in conditions of poor ventilation, and speculated that covert inflammatory disease may be instigated by the organic dusts, especially mold, in hay. 15 Others have noted that there is more mucopus in the tracheas of horses kept in poorly ventilated conditions, 25, and in one study, Thoroughbred racehorses in training, housed on straw, were found to be twice as likely to suffer from lower airway disease as those kept on shredded paper.26 More recently, Holcombe and coworkers 27showed that yearlings had a significantly higher number and percentage of neutrophils (PMNs as high as 18%) in BALF when they were stabled versus when they were at pasture. Although none of these horses had any clinical signs of respiratory disease or evidence of exercise intolerance, they were not in work, and subtle signs of performance impairment could easily have gone undetected. Dust levels in the horse's breathing zone can be as high as 25 mg/m3-a level that would be considered unacceptable by any human workplace, 28 and likely contributes to the development of airway neutrophilia as a nonspecific response to airway irritation. Increased levels of endotoxin in hay and grain dust also likely contribute to the development of airway neutrophilia. 29 It is unclear at this time whether a true allergic response is developing in these horses-whether, if we could follow the natural history of horses with IAD, they eventually become horses with a dependable obstructive response to molds found naturally in the horse's environment.
From the above sounds like its best to get the most open place from them that you can. Poorly ventilated areas cause the problem in horses predisposed to lung problems.
A few vets have used Benedryl or inhaled antihistamines to foal, but it is a gamble
