Divine right of the firstborn
A divine right to own the firstborn of people and animals. This could be because of divine deliverance of the firstborn at some time in national history, or simply by intrinsic or decreed right of the god.
Key passages
Ex 22:29–30

“ ‘You will not delay the fullness of your harvest and the juice from your press; you will give me the firstborn of your sons. You will do likewise for your ox and for your sheep and goats; seven days it will be with its mother; on the eighth, you will give it to me.

Ex 34:19

Every first offspring of a womb is for me—all of your male livestock, the first offspring of cattle and small livestock.

Nu 3:40–51

And Yahweh said to Moses, “Muster every firstborn male from the Israelites from one month and above and count their names. And you will receive the Levites for me—I am Yahweh—in the place of all the firstborn among the Israelites, and the animals of the Levites in the place of all …

Nu 8:16–18

For they are given to me exclusively from the midst of the Israelites. I have taken them for myself in place of the firstborn of every womb, every firstborn from the Israelites. For every firstborn among the Israelites is mine, both humankind and animal. On the day I destroyed every …

Dt 15:19

“Every firstling male that is born of your herd and of your flock you shall consecrate to Yahweh your God; you shall not do work with the firstling of your ox, and you shall not shear the firstling of your flock.