"Sanctify to Me every firstborn, every one that opens the womb among the children of Israel among man and among animals"Exodus 13:2.

We are commanded to sanctify all male firstborn kosher cattle and livestock – i.e., to separate and designate them to do with them as commanded in the Torah.

The kosher firstborn is given to the priest. The animal is sacrificed in the Temple, its blood sprinkled on the altar, its fats offered thereon, and its flesh consumed by the priests.

Only a firstborn in the land of Israel can be brought as a sacrifice. Outside of Israel, the animal is still holy, but can only be eaten by a priest if it becomes blemished [as it is unfit for sacrifice].

Levites are exempt from this mitzvah.