Sudden Rat Death Causes?

[guyabano]

Hello all, I was greeted today by a terrible tragedy in my rat breeding colony. I keep 4 breeder females and 2 males and about 10+ of each gender that I bred myself in "growing bins".

The last litter I bred had 11 pups and they were just weaned two weeks ago. All of them were healthy and eating on their own, drinking from the bottle. I was planning on separating them into their specific gender grow bins this weekend. I come up this evening to give them some dinner and play with them a bit as I usually do, and 6 of the 11 are dead. I don't know what could have caused this to happen. ALL my rats are fed from one food source, it comes up in a big bowl and I dish it out accordingly. None of the other bins were affected, only the one with my latest litter. I have no idea as to what might have caused it and I need some help in making sure it doesn't happen again.

The surviving members of the litter have been moved to a different, sterilized quarantine tub and are under observation.
I am gutted by this occurrence. This was my favorite litter by far to be honest. They were the most playful and open to handling. I didn't think I'd be this upset, after all they were destined to be snake food anyway. Up till that point, I still see my rats as pets.