bites

There's this arab mare named Pandora at the stable, and she's got all these tiny bumps all over her chest, and a few on her neck and rump. It looks really nasty, and this afternoon some of the bumps on her chest started to swell up. I'm not kidding, this looks really gross. It's like fly bites the size of peas (literally) and there are like a hundred of them all over her chest! could these be just thousands of fly bites, or something like hives?
 
horses can get allergic reactions that look like this. they're usually either from something in the feed or something they've rolled in. it's a funny place for her to have rolled in something - has her feed been changed recently? or has she greedily eaten someone else's feed with something new in it? if not, then they're probably fly bites.
 
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