My horse rubbed a section of her main out completely on her hay bale feeder. I rubbed/messaged the area daily. When it got warmer, I bathed her main weekly with main and tail shampoo and conditioner and mainlys restoring leave in product. Her mane grew in extremly fast with the messages and the products. It came in thick and strong. Keeping it in a running braid helps keep the hair from falling out or being pulled out.
Have you tried a mineral bath soak? Usually that and a massage work for me :)
In most situations the best thing to do is usually work it off and exercise. It gets their mind off it, warms their muscles, and allows them to stretch their joints.