I was going to swap out my whole colony with new blood but decided to pair up a few new females and a few old females every week. Now I cull based on litter size and the apparent age of the rat, if I see a female that is older and has a small litter I'll mark it for culling. My new rats seem to have smaller litters to start, probably because they are still pretty young. Once they get bigger litter sizes I'll start culling the older female rats more often. The problem now is that I'm mixing up the new and old and it's hard to tell them apart, and I'm being over run with rats LOL. But with almost 50 snakes now I can feed multiple rats to each snake and use up 100-150 rats in a single evening.

I actually separate females from the males right before they give birth or shortly after if I miss pulling them. It gives the females a break after a litter is weaned before they give birth again and helps to control the amount of rats I'm producing. And after weaning I put them in a female only tub to give them another week or two off until I pair them up again. I usually pair up between 6 and 9 females per week, that's 60-90 babies per week with an average litter size of 10. The problem is if I get all large or small litters it complicates things a bit, I'd actually rather have too many rats than not enough. Not sure what I'm going to do this fall when I have 150+ hatchlings, I may have to make an order and do frozen thawed to supplement, or buy another rat rack LOL.