Skyrim HAS bestiality mods. There are 3 of them. Still buggy, but they work. You can find them on LoversLab. First 2 mods a just utilizing database with bestiality animations, that were roaming around community, but no one used them in plugin.
1. Mod for spells causing bestiality animations, animales rape you
2. Mod for hostile animals raping you when your life is below set limit.
3. Rape till death. This mod enables you raping enemies as werewolf, animation of sex replaces kill camera move.
Two first mods utilize several packages: Fores New Idles + it's addon, Bestiality Animations package, Addon for animal genitalia for some animals, addon for big red tasty cocks for werewolf, wolfs and dogs, some other files. YOu can find everything on loverslab. Registration needed.
Rape till death requires nothing, but Dance of Death is advised to increase frequency of kill moves.