Write a fanfic where NAME_1 and NAME_2 are riding their horses in the forest. NAME_2 is riding her beautiful mare while NAME_1 is riding a massive stallion. He is a breeding stud and is extremely large, masculine and virile. He is also rippling with muscle. Even by breeding stud standards his genitals are also extremely large. Emphasise how large, masculine and muscular NAME_1's stallion is in all aspects