Negative Mitzvot 144, 108

The first-born animals must be redeemed or offered as sacrifices in the Beit Hamikdash (See positive Mitzvah 79).

The priest is entitled to portions of the meat that are not burnt.

A non-priest is not given a portion of this sacrifice.

This Negative Mitzvah applies only to a "perfect" first born animal, one that has no blemishes and is fit to be sacrificed.

This Negative Mitzvah contains two distinct laws.

The first is that a priest may not eat his portion of this first-born sacrifice outside of Jerusalem. The second is that a non-priest is forbidden to eat any of this meat at all.

At the time of the Exodus from Egypt, HaShem declared that all first-born male children and animals will be sacred to Him.

First-born male children may be "redeemed" in a special procedure called "Pidyon HaBen" (see Positive Mitzvot 79-80).

However, first-born oxen, sheep or goats are considered holy and must be offered as sacrifices. We are forbidden to redeem these first-born animals.