BestialityAh, a tale old as time itself: You, one of God's creatures, a lot of spare time and a two hearty scoops of sexual frustration. Suddenly, when nobody is conveniently around to distract you, you realize that your animal companion is equipped with relatively compatible genital equipment, and the gears begin turning.
Naturally, this situation is entirely impossible to explain to anyone if you're caught at it and they don't approve. There's nothing even close to the position to claim you were doing instead, and your lack of clothing, no matter how subtle, will be a bit tough to deflect attention from.
There aren't many statistics available on animal fucking, but based on the stories that arise, it's pretty common. Sheep, cows, dogs, horses, really most domesticated animals are potential playmates, but other, more exotic animals occasionally make the rounds. Naturally, any cases of people caught at it make the newspapers immediately, and one theme which does arise is a pattern of such activity spread across months or years... because hey, it works.
Also, don't confuse it with animal husbandry. That's an actual legitimate field of study/farming where the breeding patterns of animals are tracked to bring out the strongest traits.