Minimising Respiratory Problems Associated with Dust and Spores in Hay

By Dr Meriel Moore-Colyer
HORSES cough for three main reasons: a virus, a bacterial infection or an allergy to dust or pollen. Given time and appropriate treatment the first two causes can be relatively easily dispatched, the third however is a life-long condition and needs to be properly managed if the horse is to fulfil a useful and active life.
The most common disorder is a hypersensitivity reaction to stable dust (bacteria, fungal spirals, plant particles and insect fragments) and is known as Recurrent Airways Obstruction (ROA) formally known as COPD. The condition causes an increase in mucous secretion which can be visible as a mild nasal discharge and occasional cough to fully blown emphysema. Even if your horse is showing only mild signs of ROA it will have a reduced capacity for exercise and if asked to work hard will be considerably stressed. Clarke and Madelin in 1987 identified over 50 different species of microorganisms in the stable air, the primary source of these being the hay and bedding.

All hay contains large numbers of fungal spores but it is the small 5µm diameter or less particles that can reach the alveolar membranes. There, they are processed by resident macrophages which produce an antigenic material that in turn precipitates the hypersensitivity reaction. Many of these particles are the spores of thermophilic actinomycetes (heat-loving fungi) and have been particularly implicated in RAO. Unfortunately within the stable environment, even those very well ventilated (five changes of air per hour) the spores obey Stoke’s Law and fall with terminal velocities proportional to their diameters which mean less than 0.1cm/second. Thus the stable environment can have up to 3000 respirable particles per ml of air. Assuming a tidal volume of four litres in an average horse this can result in 12 million particles taken every breath. With such a challenge everyday it is surprising that not every stabled horse coughs.
Changing the source material is the only effective way to reduce the number of airborne particles and the soaking period commonly varies from complete submergence for several hours to a quick spray with a hose pipe. However neither regime is ideal, the former causes loss of important nutrients from the hay whereas the latter is ineffective at reducing the airborne particles. Some detailed investigations on soaking procedure were carried out by Moore-Colyer (1996) and Moore-Colyer and Blackman (1998) and their results detailed in tables one and two shown that the optimum time to soak hay was ten minutes. This duration resulted in a reduction in respirable particles of >90 per cent while minimising the loss of important minerals. However, in the latter study hay nets were also steamed for 80 minutes being being tested for airborne particle numbers and nutriet loss. Steaming proved to be just as effective as soaking in terms of reducing the respirable challenge by more than 90 per cent, but importantly it did not cause any loss of nutrients compares with the dry hay. 

From studies it is clear that steaming is the preferable method of dealing with the airborne challenge and minimising nutrient loss but the other advantage is that it does not produce ant post-treatment liquor. 
The post-soak water, even after short periods of soaking, is a biological hazard and should not be put down normal stable storm drains.
Using the HAYGAIN steamer is a very good alternative.  
HAYGAIN is currently available in three models: the HG-1000, HG-600, HG-GO and The ONE. 

For further information please contact HAYGAIN hay steamers on 0333 200 5233 or


For further information please contact Joanna van den Bos at TSM on 01724 784600.