Mineral oil, mineral oil; AND MORE MINERAL OIL! Haha!
1. Wash your horse’s mane once or twice a week, putting shampoo and a little bit of mineral oil in his mane
2. DAILY comb with mineral oil. This can get messy, but using plastic gloves should do the trick
3. With the forelock, lather it in mineral oil after you ride.
4 (optional). Coconut oil is a known treatment / cure for hair loss. If you put a few teaspoons of that in the forelock/mane/tail, it will create glossier and thicker hair.