Having commanded the sanctification of the firstborn son and the firstborn kosher domesticated animal, the Torah added the mitzva of the firstborn donkey — the donkey that is the first issue of its mother’s womb — as it is stated: “Every firstborn donkey you shall redeem with a seh, and if you do not redeem it, you shall break its neck” (Shemot 13:13). Although the firstborn donkey has sanctity, it is a non-kosher species and cannot be offered on the altar. The Torah therefore commands that it be redeemed with a seh — a lamb or kid — whereupon its sanctity departs and the donkey may be used for ordinary purposes. The seh itself does not become sacred; it is simply given to a kohen, who may do with it as he wishes. This too is one of the twenty-four priestly gifts, intended to sustain the kohanim so they can devote themselves to teaching Torah in Israel.
As long as the firstborn donkey has not been redeemed, one may not work with it or benefit from its hair. If its hair becomes tangled and causes distress, it may be cut, but benefit from the hair remains forbidden (SA YD 321:9).
A donkey may be redeemed with anything equal to its value: a firstborn donkey worth ten dinars may be redeemed with any item worth ten dinars. The advantage of using a seh is that even a seh worth only one dinar can redeem any donkey, however valuable (SA YD 321:5).
Since redeeming the firstborn donkey is a mitzva, the Sages instituted a berakha for it. The custom is to lift the seh for the sake of designating it, recite: Barukh Ata Adonai Eloheinu Melekh ha-olam, asher kideshanu be-mitzvotav ve-tzivanu al pidyon peter ḥamor (“Blessed are You, Lord our God, King of the universe, Who has sanctified us with His mitzvot and commanded us concerning the redemption of the firstborn donkey”), and then give the seh to the kohen.
If the owner refuses to redeem the donkey, since it is sacred and may not be used, he must break its neck, as it is stated: “If you do not redeem it, you shall break its neck” (Shemot 13:13). This is done with a large knife at the nape. The proper course is to redeem the donkey with a seh and give the seh to the kohen — both because it fulfills the priestly gift and because killing the donkey without purpose is unseemly (SA YD 321:12; AHS 321:2).
The sanctity of firstborns generally appears in species capable of revealing it: in human beings, who can sanctify their lives, and in domesticated animals, which can be offered as sacrifices. Kosher wild animals such as deer and gazelles, which are not brought as offerings, have no firstborn sanctity — and certainly non-kosher species have none either. The Torah singled out the firstborn donkey to teach that sanctity is hidden even within non-kosher species. That sanctity is deeply concealed and surfaces only in the firstborn donkey — not as an offering, but through redemption and the giving of its substitute to the kohen.
From this we learn that even non-kosher animals have a role in the repair of the world through God’s word. Although it is a divine decree that this concealed sanctity surfaces specifically through donkeys, the choice is not without meaning: the donkeys carried the great wealth of Israel out of Egypt (Bekhorot 5b). The donkey suggests simple materiality, which at first glance seems detached from any divine purpose. Through the sanctity of the firstborn donkey, it becomes clear that material life is meant to serve as a foundation for the revelation of sanctity — just as the donkeys bore the material wealth that later supported God’s service and the building of the Mishkan. The Sages hinted at this (Sanhedrin 98a) when they said the Messiah will ride a donkey: he will draw materiality close and make it a vehicle for the revelation of the Shekhina, so that divine ideals may be manifest in the world.
