[If] a [donkey] which had previously given birth and one which had not yet given birth [now] bore two males —- he must give one lamb to a Kohen; [if they bore] a male and a female —- he must set aside one lamb for himself.  As it states (Exodus 34:20): The firstborn of a donkey you shall redeem with a seh —- [it may be] of sheep or goats, a male or a female, old or young, perfect or blemished. He may redeem with it many times; it enters the pen to be tithed; and if it dies, one may derive benefit from it.

One may not redeem [a firstborn donkey] with a calf, an undomesticated beast, a slaughtered animal, a tereifah, a hybrid, or a koy. R’ Elazar permits [redemption] with a hybrid because it is a seh; but he prohibits [redemption] with a koy, because it is doubtful. [If he] gave it to a Kohen, the Kohen may not keep it until he sets aside a lamb or kid in its stead.