Basic reproductive behavior Horses, like most animals, depend on the sense of smell to signify the readiness of a female for an encounter. The mare will often prove recalcitrant for some time, even threatening to kick the stallion. As he squeals and nips her however, with time, she becomes acquiessent and allows him to mount her and complete the union. The Stallion A full grown stallion's cock, when fully erect, will measure some two to three feet long. It can be three to six inches thick at the base, to about two inches thick at the head.
Horses are somewhat different from other animals in the way their cock head works.
When a horse is fully erect and excited and ready to mount, his cock head is somewhat pointed and not as thick as might be normally observed. This is to facillatate an easier entry into the mare. It is thought that this serves as a plug to force the semen deep into the mare rather then allowing it to leak out. It will take quite a few spurts to accomplish this. Each time his tail will raise and lower in a brief flick.