I've used horse hair flies. I've fished the Big Lost River near Mackay, Idaho with the
Mackay Special fly. It was a very, very effective fly tied with the Pott weave using horse mane hair.
Horse hair is also used for woven patterns developed years ago in Montana. George Grant and Franz Pott developed woven flies.
I refer you to two books,
The Master fly Weaver and
Montana Trout Flies by
George Grant, both reprinted in 1981. I bought both books when they were the only way to learn how to weave flies. You can use horse hair for the woven flies.
Heres an article on Franz Pott:
Franz Pott
I believe at least some Woven Czech/Polish nymphs use the Pott weave. See Charlie Craven's tutorial on how to use the Pott weave for Czech/Polish nymph patterns.
Charlie's FlyBox - Colorado's Best FlyShop and online Fly Tying Tutorials