Reference for Bekhorot 40:14

הא איכא מיעוטא דחולבות אע"פ שאין יולדות

But R'Joshua<span class="x" onmousemove="('comment',' Who takes into consideration the minority of animals which discharge, also takes into consideration the minority of animals which give milk although they had never given birth. Therefore the offspring in this case is subject to the law of the firstling.');">⁷</span>

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