Granted that a female animal cannot be brought as a burned offering, we can assume it is a peace offering. But a male animal can be brought as a peace offering; why do we assume that it is a burned offering? The Talmud suggests a few explanations: we are really talking about a one who consecrates money, not an animal, or the teacher doesn't mean that we really bring it as an offering, or maybe we exchange its designation. In the end, the Talmud finds all of them lacking. Finally, Rabbi Yakov suggests the following: the court makes a stipulation that if a sacrificial animal is lost, then its designation by the owner becomes invalidated retroactively, and now it transpires that it always was a burned offering.
The Talmud then discussed other similar conditions that the Court made for the betterment of society. For example, if one finds an animal like the one above and returns the find to the Temple, it used to be that he would be required to bring the libations to go with it. On hearing this, people started leaving the found animals in place. The Court then stipulated that the money for the libations (wine and flour) should come from the communal funds, that is, shekalim.
Art: Landscape With Animals And A Drover Resting By A Tree by Dirk van Bergen