The She-Ass
Scholars have said that if one sees their she-ass pregnant, their wife, concubine, or servant might become pregnant. If the she-ass was under his possession in the dream and became pregnant by him, but gave birth to an offspring unlike its species, then the child belongs to someone else unless there is a sign indicating it is his. Drinking she-ass milk may signify a minor illness followed by recovery, and the birth of a foal from a she-ass could open doors of livelihood for the dreamer.
Per Ibn Sirin's Muntakhab al-Kalam fi Tafsir al-Ahlam