legal meds for horse allergies

[Mavhyjac@aol.com]

Hi   I hope someone may have some suggestions for me, I have a young endurance
prospect who has suddenly come down with bad allergic reaction to  probably
his hay. He broke out in severe hives 3 days after we got new crop hay ( from
same farm I've always gotten hay since his birth) he had a few welts last year
though not  bad enough to medicate (cleared up spontaneously in january) I
tried him on homeopathics ( apis and ledem) but he got worse by 36 hrs later
my vet put him on  azium(dexamethazone) which worked but 3 days after stopping
it his hives were back with a vengance, I didn't want prolonged steriods so
the vet put him on 2 days of steriods and antihistimines(hydroxizine) he is
cleared up and comfortable again but vet thinks this is long term problem. So
what can I use ? Any antihistimes that are legal? I am also putting him on MSM
(sulpher) and going to try slowly backing off the hydroxizine so his dose is
the lowest he can tolerate. Thoughts? Thanks,  
                                                Amy, and the lumpy spotted
Crackerjack