Responsa for Bekhorot 47:42
אפטורה דבכורה
- It refers to the exemption from [the law of] the firstling.<span class="x" onmousemove="('comment',' In that respect alone the two parts of the Baraitha are alike. For just as in the second part they are certainly exempt from the law of the firstling, as certainly the females cling to those which have now given birth for the first time, for they would not leave their own offspring and give suck to strangers, in the first part of the Baraitha also, they are exempted in the future from the law of the firstling. And in the first part, even if they are not their own offspring, they are exempted, having already given birth, since otherwise they would not have given suck to strangers. But in respect of the prohibition of killing the mother and its young on the same day, there may still be a doubt.');"><sup>24</sup></span>
Teshuvot Maharam
A. The fact that a cow yields milk is no proof that she has already given birth to a calf, for it sometimes happens, though very rarely, that a cow yields milk even though she has not as yet given birth.
SOURCES: Cr. 312; L. 187; Orhot Hayyim p. 21. Cf. Moses, Minz, Responsa 34; ibid. 35; Terumat Hadeshen 271; Isserlein, Pesakim 129; ibid. 167.