She may have a fly allergy. My girl does, although her hives have never lasted that long.
I just keep her drenched in fly spray. A fly sheet is a good option but it's just too darn hot here.
I also have a prescription for an antihistamine from my vet, but I've never had it filled because I can keep it controlled with frequent fly spray. Posted via Mobile Device
I had a gelding who was allergic to fly bites and he had the same problem. Once a week he'd get a rinse down with an apple cider vinegar solution (about 1/2 cup apple cider vinegar in a bucket then fill the rest with water) and he was fly sprayed before and after every workout or rinse down. That kept his reactions to a minimum, but last summer we had especially bad flies, so we had to give him a supplement (don't know what it was, to be honest...my friend's gelding has the same allergy and she got the supplement for our horses to share).
We have a horse in our barn who is constently coverd in fly bumps! But I don't know if there old or new.... though the poor guys owner rarely comes out so he's left just to deal with them other then fly spray when he's used a few times a week.
If you able to put a fly sheet on that would probabaly help alot. Also if you show and your horse sun bleaches or gets bites and kicks alot it will help with that as well!! ( my instructor keeps fly sheets on a few of her showies)
Also one of the other horses in my barn goes away to "summer camp" (his owner goes to the cottage for the summer and brings him with her. Lucky lady) and this year they were heading into an area that was really bad for flys. And she had him on a garlic suppliment. Though she had it in a diffrent contaner so I don't know the name of it.. sorry :S
ALSO. When I bought my boy his old owner gave me her own recipe that she use to give her horses. She said it helped to give them a really healthy and glossy coat, helped with shedding and kept the flys down. Though I havn't used it yet. I may try next year as she said she usually used it from March-October. She said it wouldnt hurt them to start in the summer though. You can get everything from a bulk food or health food store. Or around here you can anyways.
3/4 cup ground flax
1/4 cup Defaittered brewers yeast (i think that's what it said. Not the neatest hand writing. But im sure if you went to the store you could just use process of elimination and find the one with the closest spelling lol)
1/8 cup ground garlic.
The only place that has bugged (literally) my horse in past years was on his sensitive belly area. In years past it was eaten raw, but we've finally gotten on top of it this year. I've been cleaning it daily with a baby wipe, touching up the itchy spots with anti-itch cream, and globbing swat onto the entire area. He lifts his hind leg doggie style to help me get to the area. It's wicked cute.
Vinegar and witch hazel seem to work well to dry old stubborn welts from older bug bites.