Mishnayos Bechoros Perek 2 Mishnah 8

If one of his ewes had previously given birth and one had not previously given birth, and they gave birth to two males, one of the males is kept by him and one is given to the priest. Rabbi Tarfon says: The priest chooses the better of the two. Rabbi Akiva says: They assess the value of the lambs between them and the priest takes the leaner of the two. And the second lamb must graze until it becomes blemished, at which point he may slaughter and eat it. And when he slaughters the animal he is obligated to have gifts of the priesthood taken from it. Rabbi Yosei deems him exempt him from giving those gifts, as Rabbi Yosei says: With regard to any animal whose replacements are in the possession of a priest, its owner is exempt from the mitzva of giving the priestly gifts. And Rabbi Meir deems him obligated to give the gifts. If one of the animals died, Rabbi Tarfon says: The priest and the owner divide the value of the remaining lamb. Rabbi Akiva says: Since there is uncertainty to whom it belongs, it remains in the possession of the owner, as the burden of proof rests upon the claimant. If a male and a female offspring were born together, everyone agrees that the priest has nothing here, as perhaps the one that had already given birth bore the male, and the one that had not given birth bore the female, in which case neither of the animals would have firstborn status.

אַחַת בִּכְּרָה וְאַחַת שֶׁלֹּא בִכְּרָה וְיָלְדוּ שְׁנֵי זְכָרִים, אֶחָד לוֹ וְאֶחָד לַכֹּהֵן. רַבִּי טַרְפוֹן אוֹמֵר, הַכֹּהֵן בּוֹרֵר לוֹ אֶת הַיָּפֶה. רַבִּי עֲקִיבָא אוֹמֵר, מְשַׁמְּנִין בֵּינֵיהֶן, וְהַשֵּׁנִי יִרְעֶה עַד שֶׁיִּסְתָּאֵב. וְחַיָּב בַּמַּתָּנוֹת. רַבִּי יוֹסֵי פּוֹטֵר, שֶׁהָיָה רַבִּי יוֹסֵי אוֹמֵר, כֹּל שֶׁחֲלִיפָיו בְּיַד כֹּהֵן, פָּטוּר מִן הַמַתָּנוֹת. רַבִּי מֵאִיר מְחַיֵּב. מֵת אֶחָד מֵהֶן, רַבִּי טַרְפוֹן אוֹמֵר, יַחֲלוֹקוּ. רַבִּי עֲקִיבָא אוֹמֵר, הַמּוֹצִיא מֵחֲבֵרוֹ עָלָיו הָרְאָיָה. זָכָר וּנְקֵבָה, אֵין כָּאן לַכֹּהֵן כְּלוּם: