There are the kinds of rats that need to be exterminated like non-domestic, disease caring rats, and rats that bite for no considerable reason. Domestic rats are also very prone to tumors. My rat Lucy that I told you about died last year from a tumor. Her tumor got to the point where she couldn't walk or turn around to scratch her back. By the time we did that her tumor was about 2 inches in diameter, the size of a Tangerine.
Rats can also have respiratory problems.
Rats may live up to the age of 3-4 years. When rats are pregnant they may carry up to 12-15 babies at a time. Rats are pregnant for about 20 days. They go in to labor for about 2 hours and then have their babies. After mother rats have their babies they are very protective and prefer not to be touched or picked up.