Equine Penis

The equine penis (especially when flaccid) looks fairly similar to a human penis. It has a glans which is wider than the rest and a shaft that is fairly straight along its length.

Despite these similarities, there are also a lot of differences. For one thing, the entirety of its length is typically drawn back into the body by the retractor muscle. In this way, the stallion’s penis is held out of the way and protected from dirt or damage.

When examining the penis itself, one will also notice several other differences. In the approximate center of the shaft’s length there is a ring wrapping around the circumference of the penis. This is known as the medial ring and may also sometimes be referred to as a preputial ring. Most stallions require stimulation here in order to reach climax. Simply stimulating the head of their penis (or the base, as with dogs) will not likely cause them to orgasm.

Further down at the ‘head’ of the penis, it may be noted that there is a projection about the size of a fingernail at the very tip of the penis. This is known as the urethral process and it sticks out from the glans. This area needs to be cleaned very thoroughly as it tends to accumulate debris and any blockage could obstruct the flow of urine.

When the horse nears orgasm, his glans will enlarge 3-4x, forming the flare. This enables him to ensure that his semen remain inside the mare for the duration of his erection and assists to increase the chances of successful impregnation.

References

http://beastiality.club/beastiality-club-extreme-animal-sex-content/the-encyclopedia-of-zoophilia/