I have never heard of it for skin allergies or medicinal purpose period. I have seen people who have horses who like beer so they share with them if they’ve got one in their hand but personally I frown on this. I think alcohol can be destructive if not used in extreme moderation and I have this policy of not giving my horse anything, or doing anything, that I wouldn’t want handed, or done, to me. So if I wouldn’t drink out of his water source, it gets cleaned. If I look at his hay (like because it’s dusty or something) and go, “If I were a horse, I wouldn’t eat that.” he gets different hay. I wouldn’t ear that stiff saddle pad if I were getting ridden…different pad. etc. So I say if you wouldn’t use a can a day to fix your skin issue, don’t make your horse. Plus who wants to hop on a horse, regularly fed beer, point it at a jump or something, and say “alright buddy, get us over safely”? lol 😉
I have a horse with skin issues and he gets canola oil or a skin supplement (have done both and they worked nicely). You can also use special shampoo, apply medicine orally, there are shots for bug allergies too, fly sheets/masks etc….Also check that his stuff is clean. He might need his blankets, brushes, saddle pads etc to be washed.
The triple threat of riding = EVENTING! 😉