One who buys the fetus of a cow belonging to a non-Jew, or sells [one] to him, even though it is not permissible, [or] enters into a partnership with him, or receives [a cow] from him to hold, or gives [one] to him to hold —- is exempt from bechor laws; as it states (Numbers 3:13): in Israel —- but not in others.  Kohanim and Levites are liable. They were not exempted from the bechor [law] of kosher animals; they were exempted only from the redemption of the son and from [the law of] the firstborn donkey.