Well i have(had) 6 females to one male. I have breed rats in the past, stopped and started again. Recently i built a rat rack to supply my feeding needs. I succesfully breed two females then the third killed my male. I found him dead in the rack. Now i didn't clean her cage( it isn't thursday yet) and i just put him in there. Did she smell something she didn't like or...... What do i do to prevent this in the future. I don't want a lot of males so should i clean the cage before switching or put the female in the males designated cage?