Never. That's the short & simple answer.
case in point, last night I just got in a fresh batch of Pinkie Mice from Big cheese rodents. So here i go again...throwing away Pinkie mice..right?
Nope.
Hatched 6/7/14
I had 7 Hatchlings that had yet to eat...and 4 that had been limping along on mouse tails......
then, last night, it was like someone switched on the little light bulb inside their little minds.
Everyone Ate!