Temurah 13B

ודבר שאינו בא בשותפות.

and it must be an item that is not brought in partnership.

רבי אומר: למה יצא מעשר מעתה? לידון ב״תמורת שמו״ וב״תמורת גופו״.

R' Yehuda HaNasi says: Why was the animal tithe singled out of all offerings as subject to substitution now, after the halakha of substitution was stated in general? It serves to discuss a special halakha with regard to the animal tithe, that of substitution of its name. If, when the animals emerge from the pen to be tithed, the one counting them errs and calls the tenth animal the 9th and the 11th the tenth, they are both sanctified. The animal that actually emerges tenth is the animal tithe, while the 11th animal is consecrated as a peace offering. And since this halakha of a substitution of its name applies only to the animal tithe, it is necessary to teach that the general halakha of the substitution of its body, i.e., regular substitution, applies to it as well.

לומר לך: תמורת שמו ⁠— קריבה, תמורת גופו ⁠— אינה קריבה; תמורת שמו ⁠— נגאלת, תמורת גופו ⁠— אינה נגאלת.

Furthermore, the verse tells you other halakhot unique to the animal tithe: An animal that is the substitute of the name of an animal tithe is sacrificed upon the altar as a peace offering, whereas the substitute of its body is not sacrificed at all. But for all other offerings, substitutes hold the same status as the animal for which they were substituted. Another difference is that the substitute of the name of an animal tithe is redeemed when it develops a blemish, like a peace offering, and the proceeds of the sale belong to the Temple treasury, whereas the substitute of its body is not redeemed, as it is stated with regard to the animal tithe: “Then both it and that for which it is substituted should be sacred; it should not be redeemed” (Leviticus 27:33).