One thing Harem breeders don't take into account is the size and quality of the offspring litters. Yes, you will get about the same number of litters (on average) regardless if you give the breeders a break or not...but with Harem litters they tend to be fewer in number each time, smaller in size (weight) and though hard to prove would have less nutrients. (the breeder is supplying all the nutrients - vitamins, calcium, etc....as hers are depleted each litter with less time to recoop them then the next litter is shorted). Usually with Harem breeders the last litter is the worst - and results in the death of the breeder from exhaustion.

I have bred for 10+ years and done it both ways and can say from experience there is a difference in quality and output from the 2 methods.

Hope this helps.