option chosen by horses and they went on to consume more steamed hay than either dry hay or haylage within a 1-hour feeding period. Traditionally, farmers and horse owners assess hay visually and by smell; however, even well conserved hay can contain significant levels of respirable dust. Respirable dust is defined as being less than 5 µm in size and is referred by Hessel et al. as the thoracic fraction and by Art et al. and Clements and Pirie as particles that are sufficiently small enough to penetrate the peripheral airways. Effect of dust Dust in hay consists of a collection of naturally occurring dust particles which include organic plant and soil particles and potentially allergenic mould, fungi, bacteria, mite faeces, endotoxins and beta glucans, all of which have the potential to contribute to the development of airway inflammation and equine asthma. This is due to the fact horses are highly sensitive to respirable dust in hay especially to the mould, fungal spores and bacteria fraction. Exposure to these particles, particularly prolonged exposure has been shown to cause respiratory disease in the horse including equine asthma also known as COPD, broken wind, heaves and recurrent airway obstruction (RAO). When Blumerich et al., 2012 fed a group of horses diagnosed with equine asthma who normally react to dry hay, steamed hay their clinical score parameters were unchanged suggesting the steaming process has reduced the allergenic portion of the respirable dust enough not to cause a reaction in these hypersensitive horses. Researchers in Belgium discovered that when fungi is found in the horse's airways they a 3.8 times more likely to be diagnosed with inflammatory airway disease. They also analysed all forage options fed to the 482 horses in the study and found that steamed hay not only had the lowest risk of diagnosing fungi in the airways but actually lowered the risk when compared to dry hay, soaked hay and haylage. Steaming hay has rapidly grown in popularity in the last 10 years since commercially available high temperature hay steamers have been developed and is accepted as an improvement to the old tradition of soaking hay, providing significant additional benefits. At this point, most high performance horses in Europe, and increasingly America, are already being fed steamed hay on a daily basis. At the same time, the general horse population in the UK, Germany, and other European countries are increasingly being