I would guess the momma rat was low on protein and found out how to get some.
I've never lost a rat at that age due to predation and would probably switch back to Mazuri given the size of litters just to be sure.
I also supplement their food with yogurt for moms with babies, especially large litters.
I also give left over meats and other quality treats after dinner time, ok so I spoil my rats![]()