My gelding lost a lot of mane and the top half of his tail due to sweet itch last summer. On a horse forum, I found a recipe for accelerating hair regrowth. I used the shaved bridle path as my growth indicator area, which grew 2″ the first month! Two cups of olive oil with 5-6 drops of peppermint oil. Apply using a boar bristle brush to stimulate the follicle roots, then massage in with your fingers. Do this 2-3 times a week, the shampoo/conditioner on weekends. I would braid the tail once dry.
I also feed a biotin supplement, Horseshoer’s Secret, for better hooves and to promote mane/tail growth.