Priests: Revenues of First-Born of Animals or Their Substitutes
Source: TTT
Numbers 18:17, 18
But you must not redeem the firstborn of an ox, a sheep, or a goat; they are holy. You are to sprinkle their blood on the altar and burn their fat as an offering made by fire, a pleasing aroma to the LORD. / And their meat belongs to you, just as the breast and right thigh of the wave offering belong to you.
Exodus 13:12, 13
you are to present to the LORD the firstborn male of every womb. All the firstborn males of your livestock belong to the LORD. / You must redeem every firstborn donkey with a lamb, and if you do not redeem it, you are to break its neck. And every firstborn of your sons you must redeem.