A recent study at the University of Edinburgh looked at the effect of soaking hay on the dust levels in the stable. Rather than look at the dust concentration within the stable as a whole, Dr Jenny Clements and Dr Scott Pirie confined their measurements to the breathing zone - the region around the horse's nostrils.
Although all dust is unpleasant, from the point of view of respiratory disease, the important dust is that which is small enough to reach the small airways where it may cause inflammation. This is known as respirable dust. These dust particles are generally considered to be 0.5 - 5 mm in diameter.
A battery operated sampling device attached to the horse's head collar allowed the respirable dust concentration (RDC) to be measured within the air that the horse was actually breathing.
They found that simply immersing the hay in a bucket of water more than halved the average and maximum RDC in the horse's breathing zone. Soaking the hay overnight (16 hours) did result in lower RDC but the difference was not significant.
Clements and Pirie conclude that "there is probably little advantage in terms of equine respiratory health in soaking hay for 16 hours compared with simple immersion."
It is often thought that little can be done to improve the respiratory environment when two stables share the same airspace. Now it seems that this may not be correct. In a further study, Clements and Pirie showed that improving the management of one stable had beneficial effects on the neighbouring stable.
They found that changing the feed from hay to haylage, and the bedding from straw to shavings, at the same time as improving the ventilation, led to a fall in the RDC. This was apparent both in the stable containing the horse and in the neighbouring (empty) stable within the same airspace.
Respirable dust concentrations in equine stables. Part 2: The benefits of soaking hay and optimising the environment in a neighbouring stable.
JM Clements. RS Pirie.
Res Vet Sci (2007) doi: 10.1016/j.rvsc.2006.12.003