I don't think its the cage that was the problem I think its the male mouse. I think he's killing off my females! Is that even possible? There are no visible wounds on them they're just appearing dead in the cage. UGH :-( I had previously thought it was the critter trail now I put them in a new cage and its definitely not the cage. I guess this would mean that he is not breedable? He doesn't even appear mean. When the 1st female died he was taking care of the newborns. It figures he would be a nice looking mouse brown and white with fluffy type hair. I was really looking forward to seeing what his pups would look like. :-(