Handy Hint 6 - Dampen all Hay & Feed below Chest Height by Dr John Kohnke

Dry, loose hay is a major source of inhaled dust as a horse feeds.
Dampening hay by placing the biscuit in a poly-woven chaff bag, spraying it with clean water for a few seconds, then leaving it to soak up the moisture for 10 minutes before feeding can reduce dust particles by 30 times as compared to the same hay which is fed dry.
Placing it in a poly-woven bag allows it to be carried to the stable or yard feeders without an excessive loss of leaves - simply shake the biscuit and leaves from the bag into the on-ground feed bin.
If a horse is fed at chest height on a wall feeder or a rail in an outside yard, the airway cleaning fluids are unable to drain from deep within the lungs.
Studies have shown that it takes 4 hours to accumulate a sufficient volume of
cleaning fluid and mucus (in fact about 3-4 litres) to saturate the air sacs in the lower lobes of the lungs and reduce airway function.
It only takes about 15 mins of head down feeding or grazing to drain away excess cleaning fluids, inhaled particles and accumulated dust, especially after exercise or travelling.

Article courtesy of Dr John Kohnke BVSc RDA - Talking Horses newsletter