Firstborn, both Sons and Livestock are to be taken from the Levites. The Firstborn of all livestock are only to be supplied by the Levites.

Numbers 18:14. Everything devoted in Israel will be yours. 15. Everything that opens the womb in all flesh, which they bring to the LORD*, whether it is of men or beasts, will be yours. Nevertheless the Firstborn of man you will surely redeem, and the firstling of unclean beasts you will redeem. 16. And those that are to be redeemed from a month old you will redeem, according to your estimation, for the money of five shekels, after the shekel of the Sanctuary, which is twenty gerahs.