My mare broke out in tiny bumps on her neck, cheeks, and chest. It's doesn't seem to be bothering her and her breathing is normal. Any ideas how I should treat it? Her feed hasn't changed and I haven't fly sprayed or used any chemicals on her.

We had a horse that did this from fly bites, only a few and he would get big whelps all over. The vet had us give him Banamine

I had a horse that would break out in hives, GRAPE size ALL THE TIME. THats how I got started on FORCO. Fixed it and never had them again. 

My guy does this due to flies. I start him in fly gear the second I see a fly early in the spring. I started him on a feed through fly repellant this year after nothing seemed to be working the past two years I have had him and I was very surprised to see that it really helped.

I just noticed today that my horse had hives on his neck, chest and stomach ... I know in the far end of the pasture the mosquitoes are terrible because of neighbors standing water and these little black nasty flies... I usually dont turn out at dusk or dawn because they are always worse at those times it seems.. well, my horse let himself out at some point last night apparently and was in the pasture all night ... he came up this morning completely bit up. Itching and the bumps  were sensitive to the touch... I gave him a cooling bath with some medicated soap for the itching and then put his fly sheet on and he stayed the rest of the day in his stall under his fan... on his own free will... he has the option to go out into his run but he stayed put in his stall... should have listened to momma and stayed in his stall instead of being a twerp and escaping 

They just don't listen-I've told all 5 of mine at different times "if only you had listened to Momma you wouldn't be in this predicament"!!

My oldest gelding came from north AR; when I bought him 20 years ago and brought him home to the Delta, he would be a mass of bumps and welts from the flies during the summer.  It took a couple of years before it didn't happen.  Sprayed him religiously, I guess it just took him time to get use to the nightmare of our summers.  

My gelding has sensitive skin, is itchy, has had hives, etc. Flies drive him nuts. He is also allergic to alfalfa. I have auto-fly sprayers and fans in the barn for him and this supplement has helped him tremendously:  

https://www.scahealth.com/p/ultracruz-equine-skin-and-allergy-control-horse-supplement;jsessionid=FoLmowaLw8rbcX3vpWEjFLzBe9vpH0HaevndU5SdjVrXnHj6LdcT!-1566081753!1346051420!1588712375947

Thanks everyone! Sounds like fly prevention is the way to go. I just got her a fly sheet and will explore other ideas too.