Generally speaking, animals are considered muktze on Shabbat and Yom Tov. That is to say, farm animals whose normal activities are associated with melakhot – activities forbidden on those days – cannot be used. Thus, in the event that an animal is to be slaughtered for food on Yom Tov, it must be prepared or set aside for such use prior to the beginning of the holiday.
The Mishnayot on our daf discuss doves that are set aside for food on Yom Tov. Beit Shammai rules that the doves must actually be handled to indicate that they have been chosen, while according to Beit Hillel it is enough to choose them by making a statement about which ones you want. It is interesting to note that in this case, all agree that the concept of muktze exists, apparently because animals are similar to the case of drying fruit, which – as we will see at the end of the tractate – is something that everyone agrees is muktze. In the case of drying fruit, once the fruit is put out to become dried it is clear to everyone that it has been set aside and will not be eaten – or even touched – until the drying process is complete. A similar idea exists in our case, where animals are set aside specifically for work (in the case of doves, they are usually raised to be trained as homing pigeons or carrier pigeons), and cannot be used for another purpose without a clear statement before the holiday.
The Re’ah points out that this is true only of animals like doves that are not specifically raised to be used for food. Chickens or geese, for example, which are raised for slaughter, would not require such preparation. Nevertheless, according to the Yam Shel Shlomo it is appropriate to choose specific chickens or geese before Yom Tov and set them aside, as well, if they are to be slaughtered on Yom Tov.
An obvious question that comes up regarding the Gemara’s discussion of this matter is whether a person can announce before Yom Tov that the entire dovecote is set aside for slaughter for food on the holiday. Making such an announcement does not obligate one to use all of the doves, and would solve the Gemara’s concerns with which birds were actually prepared. The Rashba argues that someone who makes such a statement can successfully avoid all problems. Rabbeinu Peretz, Rabbenu Yeruham and others say that this cannot be done because no one who raises doves would plan to destroy his entire dovecote, so the statement cannot be taken seriously.