Bechoros 2:1-2

Bechoros 2:1

If a Jew buys the unborn offspring of a non-Jew’s cow, of if he sells it to him even though this is prohibited, or if he owns it in partnership with him, or if he receives it from him to raise, or if he gives it to him to raise – in all of these cases, the Jew is exempt from the law of firstborn animals. This is because Numbers 3:13 specifies that this rule applies “in Israel,” to the exclusion of others. Kohanim and Leviim are obligated. They are only exempt from redeeming a firstborn son and a firstborn donkey; they are not exempt from redeeming a firstborn kosher animal.

Bechoros 2:2

All consecrated animals that developed permanent blemishes before they were consecrated and were subsequently redeemed are subject to the laws of firstborn animals (i.e., if they give birth to a firstborn) and the portions given to a kohein; they become secular so they may be shorn and used for work. Their offspring and milk are permitted after they have been redeemed, one is not liable for slaughtering them outside the Temple, and the concept of substituting doesn’t apply to them. If such an animal died, it may be redeemed except for a firstborn animal and animal tithe.