So, I feel like some extra context is required here.
References to animals appear not infrequently in Mesopotamian love magic, in particular bulls, stags, dogs, goats, etc. I've seen different scholars put forward different theories as to why this is; some suggest it's to channel the spontaneous, aggressive mating of wild animals, while others such as Gwendolyn Leick in Sex & Eroticism in Mesopotamian Literature suggest that "the copulation of animals, imagined or actually observed, was certainly considered arousing." Leick goes on to discuss the passage I posted above, saying:
Here a woman's voice is speaking. This does not mean that she wants the spell to work for herself. Rather, she is used here to dramatize the erotic fantasy element of the spell. She speaks to the famously excitable male animals to arouse their ardour, first suggesting that they mount each other, the ass the jenny, etc. then, building up the sexual tension, the male animals are 'tied to the bed' and now she invites them to copulate with her.
It should be noted that spells such as these aren't love spells as we think of them, but are instead incantations for dealing with various forms of sexual dysfunction. Other incantations from Biggs's Texts From Cuneinform Sources make this more obvious:
Wild ass who had an erection for mating, who had dampened your ardour? Violent stallion whose sexual excitement is a devastating flood, who has bound your limbs? Who has slackened your muscles? [...] Incantation for potency. It's ritual: you crush magnetic iron ore, pit it into oil; He should rub his penis, chest, his waist, and then he will recover.
The context of these incantations always makes them a good bit more interesting to me. They weren't just hand-wavy magic spells; if you imagine them as as essentially ritualized couple's therapy, the repeated and graphic descriptions of vulvas, penises, animal matings, etc, starts to make more sense. I don't think they had fuzzy handcuffs and sex-activity-dice in Babylonia, so this is what you got.
