Reference for Bekhorot 4:49

לכשתלד דלא מקבלת זכר

[It is] because it cannot be cured, and therefore it is as if he had sold it to be slaughtered.<span class="x" onmousemove="('comment',' Therefore there can be no fear that one might substitute another animal which is not to be slaughtered and sell it to a gentile.');">²⁹</span>

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