I am having a hard time breeding my rats. My mice are breeding just fine but my rats are doing nothing. I have taken them out of the cage for a few weeks, put them back together for about 3 weeks before taking them out again. Even tried leaving them in there for over 2 months. Still I am getting nothing. I have at least 6 inches of substrate in their cage to give them a place to have the babies. They have plenty of food and water. What am I doing wrong?