Inbreeding, how many generations should be skipped?

[SlitherinSisters]

I've bred rats for 16 years. Normally, I choose males from separate bins than females and develop colonies at earliest age possible. I don't rotate males nor do I use birthing racks. Only time I use any separate rack are grow out racks.

I produce 1100-1500 rats per week normally.

Holy moly that's a lot of rats!

I breed the already inbred ones.

I usually breed 2 generations maybe 3, I always old back some of the females I produce for future breeder (I hold them back based on temperament of the mother and whether or not the mother is/was a good breeder) and every 16/18 months or so I retire the males and buy some new ones to add new blood in.

So I don't really count I just have that routine going

I haven't added any new stock to my rat colony in about 5 years. I've got friends who haven't added new breeding stock in almost 20 years. Adding new individuals also adds the diseases that they have which your current colony may not have any immunities to.

Ok cool. I really don't want to bring more rats in. Last time I brought home a new rat I lost 15 in the course of a month.