Shekalim, Chapter 7, Mishnah 4. In the previous Mishnah we dealt with meat that was found in certain places - whether in the Beis HaMikdash, in Jerusalem, or outside it. In our Mishnah we discuss a case where a live animal is found.
"Behemah shenimtzeis miYerushalayim ve'ad Migdal Eder, uchemidasah lechol ruach":
Any animal found in the area between Jerusalem and the place called Migdal Eder, and likewise within that same distance from Jerusalem in every direction - its law is as follows:
"Zecharim - olos" - if male animals are found, we assume that they were consecrated as burnt offerings, since an olah comes only from a male.
"Nekeivos - zivchei shelamim" - if female animals are found, they cannot be burnt offerings, since an olah does not come from a female, but they are fit to be peace offerings. Therefore the presumption is that they were consecrated as a shelamim offering, and they may be brought as such.
"Rabbi Yehudah omer: haRa'ui lifsachim - pesachim, kodem laregel sheloshim yom":
In the opinion of Rabbi Yehudah, any animal that is fit to be a Pesach offering is presumed to have been consecrated as a Pesach offering. These are the conditions under which it is fit for that:
That it be male.
That it be within its first year.
That it be a sheep or a goat.
And when does this presumption apply? During the thirty days preceding the festival. Within thirty days before Pesach, any animal that could serve as a Pesach offering is assumed to have indeed been consecrated for Pesach.
In summary: In this Mishnah we learned the law of an animal found in the area between Jerusalem and Migdal Eder, and within that same distance in every direction: males are presumed to be burnt offerings, and females are presumed to be peace offerings, since an olah does not come from a female. And in the opinion of Rabbi Yehudah, an animal fit to be a Pesach offering - male, within its first year, a sheep or a goat - is presumed to be a Pesach offering, provided that it was found during the thirty days preceding the festival.