Reference for Keritot 49:21

לא נשתמיט תנא דנשמעינן עגלה בשחיטה כשרה דתימא ר"ש היא

Now, if it were forbidden in its lifetime, how could it go out to pasture among the flock; surely it was forbidden while still alive?<span class="x" onmousemove="('comment',' I.e. , how can it revert to its profane status after it had been brought down to the 'rough valley' as the heifer whose neck was to be broken and so unfit for use.');">¹²</span>

Jastrow