I have some females that are well into their second year of breeding with no problems.
I think the biggest key is to give them some time off after you wean the litters so they can get their bodies back to health.
If you plan on keeping all your females together then they will never get a break because they will be helping the other mothers.
Your best bet is a rack, say 7 tub.
3 to 4 females per tub in the top 4 tubs
the male gets tub 5 as his own (I would have at least 2 males)
male in tub 1 for 2 weeks then move male to tub 2 and so forth
when the male gets to tub 5 he is on his break as well.
bottom two tubs are for your male and female wean outs
This will work on a small scale but you will get to a point that you might have to start freezing off litters too.
Plus with the rotation of tubs you will almost always have different size "meals" for all of your collection.
It does take some time to get it running right.
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