תּוספֿתּא אויף במדבר 18:17

Out of all the unclean domesticated animals, there are none that are liable in [the laws of] the first-born except for a donkey. Out of all the unclean wild animals, there are none that are forbidden on account of their sale-price [to donate to the Temple] except for a dog (Deut. 23:19). Rabbi Meir used to say, [as to] anyone who fulfills the commandment of the first-born donkey, they treat him as though he has fulfilled the commandment on behalf of every unclean domesticated animal, and [as to] anyone who disregards the commandment of the first-born donkey, they treat him as though he has disregarded the commandment on behalf of every unclean domesticated animal. Rabbi Yosei HaGalili says, behold, it says (Num. 18:17), "But a first-born bull or a first-born sheep or a first-born goat shall not be redeemed, [for] they are holy." A first-born bull: [The obligation does not apply] unless the birth-mother is a [female] bull and the offspring is a bull. A first-born sheep: Not unless the birth-mother is a sheep and the offspring is a sheep. A first-born goat: Not unless the birth-mother is a goat and the offspring is a goat. And if [the offspring] has even a few signs [of its species] similar to its mother, it is liable in [the law of] the first-born.