Avodah Zarah 22 - Idolaters and Animals
Bestiality is forbidden under seven Noahide laws, as follows from " Therefore, a man shall... cling to his wife and they shall become one flesh (produce offspring) " - which excludes an animal, with whom man does not produce offspring. However, in the ancient times among pagan nations bestiality was widespread, and therefore...
We may not stable an animal in the inns of idol worshippers, since they are suspect in regard to bestiality. Anyone who leaves an animal at their disposal would violate "do not put a stumbling block in front of a blind man."
However, following this logic, we should allow to place female animals with female idolaters? No! This was prohibited, because idol worshippers commonly consort with their fellows' wives and sometimes an idol worshipper visiting his paramour will not find her at home, but may find a Jew's animal there, and sodomize it, since they preferred Israelite's animals to their own wives. This made sense, since his own animal might become sterile, and with someone's wife he might be discovered, thus the Jewish animal was the most defenseless creature.
Art: Julien Dupre - The Young Shepherdess