I supposse it depends on the animal facility cleanness, but I have had Rag2 mice in a conventional room without problem (I don´t remember how much time) because a mistake of the animal facility staff.
Agree to David! Also you can interchange water plus antibiotic and acidified water (with HCl) every 3 days. Hope, you will have no problems several months.
Thanks for all replies. Specifically, we need to know that because we would like to challenge these mice in natural conditions (conventional room) for protection experiment with some molecules which are implicated to cure infectious diseases. But first, we need the survival or any symptoms for estimate how long protect or have effect our compounds in "knockout B cell-deficient mice".