it might help,but he might also get hurt by something,run off,get stolen,hit by a car,anything really,unless you are going to crate him and check that he is ok alot,I dont advise it.
if it has air it should be ok (you have to open the top of the bag) but you need a big fish tank for him,they need at the very very least 10 gallons,but that breed does better with 20-30 gallons. (on an off note,I hate that they give animals away as carnival prizes,totally inhumane)
if your trying the little pellets,I would try flakes,he might be used to flakes,and the pellets hurt his mouth,or he might be old and they hurt him,if your using flakes,try pellets,he might be used to those...
Quarter horses are mostly used for barrels cause they were bred to be fast for a short period of time,theyre called the "quarter horse" because theyre the fasts horse,but only for about a Quarter of a mile,theyre also Americas most popular breed,so thats another reason,they have strong hind ends...