The most common disorder of the
esophagus is an obstructive disorder commonly referred to as choke. The
clinical signs include stretching of the head and neck, restlessness,
drooling (or excessive salivation) attempts to swallow that may result in
coughing, a feed-tinged discharge from the nostrils, bad breath, and
possibly a lump at the site of obstruction. Choke may have many different
causes, e.g., feed, wood, or foreign bodies.
Sometime the discharge can be greater, when choking on chemically cured alfalfa it is more rapid and green in color. Usually horses get over it by themselves.
common predisposing factor for choke is improper mastication (chewing).
Causes of poor mastication include poor teeth in older horses, erupting
teeth in younger horses, greedy eating, exhaustion, and depressed
swallowing reflexes from general anesthesia (as would occur following a
surgical procedure). Other possible causes include a narrowing (stricture)
of the esophagus, and tears or outpouchings (diverticula) of the esophagus
that become impacted and occluded with feed.
During the last year I came across seven cases of choking, all of them on pelleted feeds. The pellets will turn back into fine powder while chewed by the horse, sometimes resulting in choking, usually due to insufficient moisture (saliva) in the food passing into the esophagus and getting stuck in form of dough like mass. Hence, pay attention especially after hard work when the horse's system was depleted of water. Preferably feed mash in such cases. The fine chemically cured alfalfa, when fed after strenuous exercise (race) when the depletion of water is significant, will also increase the chances of choking. Most horses that choked did not have free access to hay.
All my comments are merely my opinions and beliefs gained from 40 years of professional life with horses. All drugs should be used only by the consent of a veterinarian and according to his instructions. A person who is with the horse everyday, should know him better than anyone else.