Rashi says the reason you work an animal, like an ox or donkey and feed it (and not sell it right away) is because there's a value to returning the same, trained animal that is familiar with its owner. Mashma that we would NOT bother the finder to do that if there was no advantage of being returned the very same animal, even if the living thing could produce. Yet we see that by a hen, we consider it like a large animal, i.e. a cow or donkey, and you have to work it and feed it for 12 months. Why?
Daniel Steinberg, Columbus, OH USA
Daniel, Baruch she'Kivanta. Your question is asked by the Netziv of Volozhin!
1) This is in his Sefer Emek ha'Netziv, on the Sifri on Devarim 22:3 (DH v'Chen Ta'aseh l'Chamoro, page 250 of the Sefer). He asks on Rashi on the Mishnah 28b: why does Rashi write that the animal already knows the owner who has taught it to do as he wants -- how is this applicable to the Halachah concerning a hen, which does not do any work but merely produces eggs and meat?
2) I would like to suggest an answer to the Netziv's question with the help of another statement of Rashi later on in Bava Metzia (93b, DH l'Kushra d'Chayuta). Rashi writes that the advantage of keeping the same animals is because the owner knows them already. However, Rashi then adds two important words: "u'Lemudos b'Veiso" -- literally, "they have learned to be in his house." In other words, the hens are accustomed to the house and feel "at home." We see from this that if the hen is familiar with conditions in the houesehold, she will produce better eggs.
Kol Tuv,
Dovid Bloom