How do I properly thin a very thick mane? Do I thin from the underside or on the top side?

When thinning a horse’s mane, start with the longest hairs. Pulling the longest hairs will help get the mane to the desired length and thin the mane at the same time.
You will need a comb. If you are right-handed, take a small pinch of the longest mane in your left hand and with your right hand holding the comb, comb against the mane section you are holding to sort of tease the hair back. Then wrap the remaining hair …