Mishnayos Bechoros Perek 3 Mishnah 1

In the case of one who purchases a female animal from a gentile and does not know whether it had previously given birth or whether it had not previously given birth, and after the purchase the animal gave birth to a male, Rabbi Yishmael says: If the mother was a goat within its first year the male offspring certainly is given to the priest, as it definitely never gave birth previously. From that point forward, i.e., if the mother is older than that, its offspring’s status as a firstborn is uncertain. If it was a ewe within its second year the male offspring certainly is given to the priest; from that point forward an offspring’s status is uncertain. If it was a cow or a donkey within its third year the male offspring certainly is given to the priest; from that point forward the offspring’s status is uncertain. Rabbi Akiva said to him: Were an animal exempted only by giving birth to an offspring and in no other manner the halakha would be in accordance with your statement. But the Sages said: An indication of the offspring in a small animal is a murky discharge from the womb, which indicates the animal had been pregnant, and therefore exempts subsequent births from the mitzva of the firstborn. The indication in a large animal is the emergence of an afterbirth, and the indication in a woman is a fetal sac or an afterbirth. Since these can be produced even within a year, it cannot be assumed that an animal in its first year is definitely subject to the mitzva of the firstborn. Rabbi Akiva continues: Rather, this is the principle: In any case where it is known that the animal had previously given birth, the priest has nothing here. And in any case where it is known that the animal had not previously given birth, that is given to the priest. And if it is uncertain, it may be eaten in its blemished state by the owner. Rabbi Eliezer ben Ya’akov says: In the case of a large animal that expelled a mass of congealed blood, that mass must be buried. The reason is that perhaps there was a male fetus there which was consecrated as a firstborn when it emerged, and the animal is exempt from having any future offspring counted a firstborn.

הַלּוֹקֵחַ בְּהֵמָה מִן הַנָּכְרִי וְאֵין יָדוּעַ אִם בִּכְּרָה וְאִם לֹא בִכְּרָה, רַבִּי יִשְׁמָעֵאל אוֹמֵר, עֵז בַּת שְׁנָתָהּ וַדַּאי לַכֹּהֵן, מִכָּאן וְאֵילָךְ סָפֵק. רָחֵל בַּת שְׁתַּיִם וַדַּאי לַכֹּהֵן, מִכָּאן וְאֵילָךְ סָפֵק. פָּרָה וַחֲמוֹר בְּנוֹת שָׁלשׁ וַדַּאי לַכֹּהֵן, מִכָּאן וְאֵילָךְ סָפֵק. אָמַר לוֹ רַבִּי עֲקִיבָא, אִלּוּ בַּוָּלָד בִּלְבַד בְּהֵמָה נִפְטֶרֶת, הָיָה כִדְבָרֶיךָ, אֶלָּא אָמְרוּ, סִימַן הַוָּלָד בִּבְהֵמָה דַקָּה, טִנוּף. וּבְגַסָּה, שִׁלְיָא. וּבְאִשָּׁה, שְׁפִיר וְשִׁלְיָא. זֶה הַכְּלָל, כֹּל שֶׁיָדוּעַ שֶׁבִּכְּרָה, אֵין כָּאן לַכֹּהֵן כְּלוּם. וְכֹל שֶׁלֹּא בִכְּרָה, הֲרֵי זֶה לַכֹּהֵן. אִם סָפֵק, יֵאָכֵל בְּמוּמוֹ לַבְּעָלִים. רַבִּי אֱלִיעֶזֶר בֶּן יַעֲקֹב אוֹמֵר, בְּהֵמָה גַסָּה שֶׁשָּׁפְעָה חֲרָרַת דָּם, הֲרֵי זוֹ תִקָּבֵר, וְנִפְטְרָה מִן הַבְּכוֹרָה: