What, if anything, do you give for coughing?

[Ludi-doodi]

Is there anything you can give for a coughing horse? Yesterday my horse has begun coughing - it sound dry, like a tickle in the throat. It's not lots but noticeable and again this morning. My horse seems fine in himself and appetite is normal. Obviously, I'll keep an eye on it and call a vet called if it doesn't improve in a day or two, but in the meantime I just wondered what, if anything I can give him.

A bit of background:
For the last year following a breathing problem he's been on the maintenance level of NAF respirator boost and his hay is steamed in a net then emptied into a haybar. I dampen his feed, he's on shavings on rubber matting and has both a big trug of water and an automatic drinker, so plenty of access to water.

Oh - He's in a barn divided into four and the horse behind him has been coughing for weeks now Same sort of dry, tickle type cough.

 

[be positive]

If he is affected by an allergic reaction to dust or similar, is there another horse in the barn that gets bedded on straw or dry hay that could be enough to trigger a reaction.
It could be a virus that is causing it, although several weeks is usually enough for it to have run its course.
I usually put mine on a course of ventipulmin, from the vet, I find this much more effective than any supplements that are available, I had one horse that was always a little inclined to cough on hay, he stopped completely after a winter on haylage.