I decided to breed my My own mice once buying feeders from the local chain pet stores became too expensive. I did all the research and I purchased two female mice, and kept them together for about four months before introducing the male to them. Before I introduced the make I would try to catch them in heat to see if they were on the same cycle, but I couldn't really tell if they were or not. After keeping them together for four months I decided to introduce the male, and I kept them together for 16 days. On the 16th the day I separated them, and I noticed one mouse was considerably larger than the other. She was further along in the pregnancy then the other female mouse. When I did all the research about breeding mice I read that if one mouse has her babies earlier than the other then the second mouse might kill her babies when she has them because they are considerably smaller, and it will lead her to believe that they are sick or unfit to survive. So what should I do? Should I separate the two females into separate tanks? Although that might put the stress on them, being a single mother, and cause them to kill their babies. Should I just keep them together and hope that everything will be okay?