Because I want to breed for longer life, and because it's a longterm issue, there are several ways to help me gain a head start.
Selecting healthy parents: I'm trying to use parents who have not had any chronic illness, and have not had several instances of different illnesses.
Selecting parents with a family history of longevity: In the long run I would like to use rats whose ancestors come from litters with a longer lifespan.
Selecting neophilic parents: Rats which are unafraid and interested in new objects and experiences produce less stress hormones, and tend to live longer, than neophobic rats. I would like to breed from rats that are bold and calm, not jumpy and scared of new experience.
Selecting active parents: I'm trying to breed from rats who remain active as they age, and don't become 'hammock potatoes'.
Selecting parents who are not overweight: Obesity increases the risk of mammary tumours and other conditions. I would like to breed from fit and trim rats.
Selecting loving, people friendly rats: These are the rats who are a joy to own. They're well adjusted and happy with their lives. I'm not talking about clingy, dependent rats, but those who are sociable and confident with people as well as with other rats. I don't know if this quality affects their lifespan, but it certainly affects their quality of life because they will form a closer bond with the owners who care for them.
Inbreeding to produce consistent results: I plan to bring my rats into one line by breeding uncle to niece or cousin to cousin where possible. I need to inbreed to produce a 'line' with predictable qualities. By keeping a reasonably large number of breeding rats I should manage to give myself enough scope for selection to compensate for my relative inexperience. By breeding two pairs at a time I can give myself more options for selection in the future.
There's been a lot of criticism in the media lately regarding inbreeding. When I first began looking into breeding I was undecided, but having read the books and listened to more knowledgeable breeders my mind is made up. My view is that it is actually more ethical in the long term to inbreed when coupled with ethical selection. The marvel of inbreeding is in the fact that it uncovers any problem genes so that I can avoid breeding from rats that express them and related rats, rather than covering the problem and allowing the genes to spread through the rat population until they reach the point where they are widespread and come out unexpectedly later, and it allows me to reinforce the positive genes giving me a method of achieving my breeding aims.
I am beginning a second line which will allow me to outcross to a known line for the foreseeable future, or which will replace my original line if any serious problems arise.
Outcrossing, Linebreeding and Inbreeding in Rats (An Introduction)
The benefits of inbreeding.