The first thing is to dampen the hay to eliminate all the dust.
The main disadvantage of this system is the significant decrease of the hay eating quality.
You should have to be very extremly vigilant to choise a food who cover all his needs.
His emphysema don't make the type of food, but do not hesitate to dampen the food with a spoonful of olive oil, wich will allow for control the potential residues in food.
For the feed, you can find in the range of Destrier, two feed without dust for respiratory allergy horses or sensibilities.
Fibrissimo : feed, dusting, compacted on cubes, to distribute dry or moistensec to create a fiber pastry.
Fibr'alfa : dusting feed with long fibers.