You can use human shampoo, but it would make your horses mane, tail, coat healthier if you bathed him in apple cider vinegar.
No it won't burn him.
It won't irritate scratches, it will actually heal them so much faster.
It won't make him smell like a pickle.
You can actually give it to him as a supplement, and it will make him healthier.
You won't believe the results!!!!!