Study Bekhorot folio 53B with parallel Hebrew-English text, traditional commentary, and modern study tools. Free access to Babylonian Talmud online.
Text Excerpt
אפשר כדרב יהודה, דאמר רב יהודה: מותר לו לאדם להטיל מום בבכור קודם שיצא לאויר העולם. הכא נמי, אפשר דשדי ביה מומא מעיקרא!
The Talmud explains that it is possible to act in a different manner, so that the priest does not lose out on his rights to the firstborn animal. One can act in accordance with the opinion of R' Yehuda, as R' Yehuda says: It is permitted for a person to inflict a blemish upon a firstborn animal fetus before it emerges into the air of the world. The Talmud challenges: If so, here too, it is possible for one to inflict a blemish from the outset, before the animal becomes consecrated as the tithed animal.
מי ידע הי נפיק? וכי תימא דמפיק ליה בריש עשרה — ״לא יבקר בין טוב לרע״ אמר רחמנא.
The Talmud answers: How can one know which animal will emerge as the tenth? Since it is impossible to know this, one cannot inflict a blemish on the animal before it becomes consecrated. And if you would say that one should bring out the animal upon which he has inflicted the blemish at the head of the 10 animals to ensure that it will be the tithed animal, this is not a valid option, as God states: “He should not inquire whether it be good or bad” (Leviticus 27:33). This means one may not plan in advance which animal will be the tenth.
וכי תימא: אפשר דשדי ביה מומא בכוליה עדריה — מהרה יבנה בית המקדש, ובעינן בהמה להקרבה וליכא.
And if you would say it is possible to inflict a blemish on the entire herd of animals and thereby ensure the tenth one will be blemished, that is also undesirable. The reason is that soon the Temple will be rebuilt and we will require animals for offerings, and there will be none remaining without a blemish.