I have been around horses for quite some years but I have never heard this allergic reaction described as hay fever (as in the same problem that humans suffer with). I don't get it myself, for which I am very grateful, but I do have friends that do, and can see the misery it causes, so I can assume that it is equally uncomfortable for a horse. Although the season is closing, I thought I'd still take a look at what it's all about so you can be on the lookout for it nest year. Apparently it's a fairly common condition seen in young and old horses alike, and it's an allergic Respiratory Disease.
Unlike humans, horses that have allergies tend to show more flu like symptoms and less sinus and nasal effects. Their lungs become inflamed and are more likely to get viral and bacterial infections. The horse owner sees this as frequent (recurrent) 'chest colds' that the horse never quite gets over, as I did, before I heard that it was in fact a form of hay fever. Other symptoms include coughing, a lot of eye discharge and they get tired easily. There are many causes of allergic Respiratory Disease but some are more common. Several types of mould spores and weeds found in otherwise high quality hay or straw seem to bother many horses.
This is a seasonal thing, so for the horse at pasture the problem may only be seen in spring and summer. However, hay that is taken from local fields can be a year round problem. Each year, the horse usually shows more symptoms as its reaction to the problem gets stronger and stronger. Treatment of this problem can be as simple as keeping your horse outside where air circulation is available (fresh air versus stagnant dust filled air). If your horse must stay in the stall most or all of the time, try to store your hay in a separate place and ensure good airflow in the barn.
If it is cold, put a blanket on the horse and soak the hay fed to the horse in water first. If the problem is not taken care of by the above steps, then you need to speak to your Vet. To find out the cause, the vet can do a simple procedure that looks at the fluid and cells in the horse's lungs to see how bad the allergy is.
Secondly, there is a relatively new blood test that can specifically determine what 'things' the horse is allergic to and allows them to find a 'customized' treatment for that individual horse. Other general treatments include corticosteroids (cortisone) and bronchodilators (like those taken by human asthma patients). The important thing to realize is that recognizing your horse has this problem is more than half the battle. Once that is done, proper treatment can dramatically improve the usefulness of your horse.
I was very grateful when it was pointed out to me, although I will admit to feeling a bit stupid at the time. However now I know what it is, I can deal with it, so a little stupidity has bought me some knowledge that I can now use to keep my beautiful horses in better health, so that's a price I will gladly pay any time.
Roger Bourdon's aim is to bring the joys of horseback riding to everyone with his books and website at http://anyhorsebackriding.com where you can get really cool free hints and tips on learning to horseback ride