how long to use a feeder rat for breeding?

For you who breed your own rats; how long do you use a typical female rat for breeding before feeding her off? I have had two females for about half a year now and their litters have steadily decreased; they were having litters of twelve or more, and now each one has about 8 or 9 and it honestly seems like they are not growing as fast as the earlier babies. I am feeding them the same as I have in the past, but I think that maybe they are becoming "used up" after a lot of breedings, perhaps?

I suppose this is kind of a late reply.. (I just thought I'd see if I could answer anyone else's questions while I wait for mine to be answered on my thread)

Anyway, typically you feed breeder rats off to your snakes after a year, but if she's not having enough babies anymore, you may just want to start with a new female.

Another thing to consider.. does she have litter after litter, or do you give her a little rest in between? If she feels a little bony or underweight, the litters may be taking too much out of her, resulting in smaller litters.

maybe just buy a new female and give your females you have now a little break :) , just a suggestion

I understand that after 15 months or so, their fertility goes down and they should be fed off. Sounds like you got a bonus month or three out of them. Not sure where i got that from, but it seemed like a reliable source at the time.