I on the other had have had very good luck with communal mothering, seems like about every tenth litter or so i will find two females who will try to "steal" babies. Actually watched them circle around a tub when one mother would go get a baby the other would hurry and go get the one she had stolen so they moved rats from one litter to the other and back for several minutes. But have noticed that when two mothers are in the groove that they both share the duties well enough that neither mother ever looks as exhausted as i have seen with one mother with a decent sized litter. Another aspect i like about doing it this way is some first time mothers bodies just dont seem to handle the draw of babies as well as older females, and so its much easier to adopt these babies onto more suitable mothers.