Situation The first-born male baby of a female kosher domestic mammal or of a female donkey, if completely owned by a Jew, is a petter rechem (which may not be used for any purpose).
What To Do Before the mother has her first baby, sell part of her to a non-Jew so the firstborn will not be wholly owned by a Jew and, if male, will not become a petter rechem. Rabbinic guidance is recommended!