Because it is written (Devarim 12:6) "And you shall bring there your burnt-offerings and your sacrifices … and the first-born of your herds and flocks," I might think that he must bring them (the first-born) to the Temple; it is, therefore, written (Exodus 13:2) "in man and beast, he (the first-born) is mine." The first-born of a beast is likened to the first-born of a human being, and the first-born of a human being, to the first-born of a beast.