It is recommended that you breed your rat's when the doe is younger than 1 year, but older than 4 months.
Once a female rat is 4 months, she can breed.
A dumbo ratIS a fancy rat, so of course they can interbreed. The dumbo refers to the rats ears: a little larger and set further and flater on the rats head. The dumbos also tend to be larger, and, it...
From what I have read, Rats eat mice, so I wouldn't recommend putting the two together!
six to seven weeks
Rats can't vomit.