177:14 If a non-Jew owns an animal in partnership with a Jew, or if a Jew receives an animal from a non-Jew to raise with the understanding that they will share the offspring, these animals are exempt from the mitzvah of first-born animals. This is because Exodus 13:2 says, "whatever opens the womb among the children of Israel," meaning that the animal must belong entirely to a Jew. If a non-Jew receives an animal from a Jew to raise with the understanding that they will share the offspring, many authorities feel that this doesn't affect the obligation of first-born animals. If the Jew wants to exempt himself in such a case, he must sell the mother to the non-Jew.

177:15 It's a mitzvah to sell the clean animal to a non-Jew, or to enter into a partnership on it with him before the animal gives birth, in order to exempt the animal from the mitzvah of first-borns. Even though one is preventing the offspring from acquiring the sanctity of first-born animals, this is preferable to risking the possibility that he may come to shear or work the first-born. If one sells the animal to a non-Jew as a fetus, it doesn't help because one is not able to sell something that does not yet exist; rather, he must sell the mother to the non-Jew.

The transfer of ownership should be handled as follows: the Jew agrees with the non-Jew on the price of the cow. He also rents him the place where the cow is standing. The non-Jew gives the Jew a perutah (a small coin) and the Jew says to him, "With this perutah, you acquire the place where the cow is standing; that place acquires the cow for you." Or they may do as follows: after the two parties agree on the price of the cow, the non-Jew gives him a perutah and then pulls the cow onto his property or into an alley; he acquires it through the combination of pulling and money. Even if he later returns the animal to the Jew's domain, it is of no consequence.