Lenny's Mod Loader is required!

Simply copy the .ymt files into the "Stream" folder of "lml". Horses include:

Red Roan Breton
White Blagdon Gypsy Cob
Splashed Bay Gypsy Cob
Splashed Piebald Gypsy Cob
Blue Roan Missouri Fox Trotter
Black Overo Mustang
Chestnut Overo Mustang

Also try using MaVeRicK's Better Horses Mod. 
These horses have awesome stats utilizing his mod as I replaced horses that his mod works with.
https://www.nexusmods.com/reddeadredemption2/mods/842