If a Jew has a female-donkey that gives birth to a firstborn male, it is a mitzvah to redeem it. With what do you redeem it? With the young of sheep or goats whether male or female, whether large or small, whether perfect or blemished; provided it is not a treifa,¹ it is not slaughtered, and is not a ben pekuah.². This lamb must then be given to the kohein. From when are you obliged to redeem it? At anytime from the day it was born until it dies. However, it is a mitzvah to redeem it immediately, in order not to delay the performance of the mitzvah. After it has been redeemed it remains in the owner's possession, and is no longer considered sacred. Also the lamb in the possession of the kohein is not considered sacred.

footnotes: ¹ See Chapter 177, footnote 4. ² When a cow carries an unborn calf, the slaughter of the cow is considered the slaughter of the calf as well, and thus the calf, although alive, does not require further slaughtering. This type of calf is called a ben pekuah

Immediately, upon setting aside the lamb to be exchanged for the firstborn donkey, the firstborn donkey is considered a secular item even before the lamb is given to the kohein. Therefore, as soon as the lamb is set aside, this berachah is recited: Asher kidishanu bemitzvosav vetzivanu al pidyon petter chamor "Who has sanctified us with His commandments, and has commanded us concerning redemption of the firstborn donkey."

Before it is redeemed, it is forbidden to have any benefit from it, even if it was already given to the kohein. Even the kohein is forbidden to use it until it is redeemed and has taken the lamb for himself. If it died before it was redeemed, it must be buried

If the owner chooses not to redeem it, he strikes it with a hatchet on the back of its head, until it dies, and then buries it, as it is forbidden for use. The mitzvah of redemption takes preference over the mitzvah of breaking its neck.

Kohanim and Levites are exempt from the mitzvah of redeeming the firstborn of their donkeys. The daughter of a kohein or Levi are also exempt, but their husbands are obligated to redeem the firstborn of their donkeys. Partnerships with a kohein or a Levite, and also partnership with a Gentile, are exempt from the mitzvah; but it is forbidden to form a partnership with them, or to sell it to them in order to nullify its sacredness, since this may be achieved through redemption or by breaking its neck.