If the doe is in good condition, producing enough milk for the litters, etc... there's no reason you can't breed them close together for a few litters. It's natural for rabbits to breed that way. Some does and even some entire breeds though do not hold condition well because the breeders have not been concerned about breeding them so close together. Our mini rex are much worse at back to back breedings than the meat rabbit breeds. Some of the mini rex does do require a month or 2 break between most litters because they won't hold condition well, produce enough milk, or they'll pluck themselves bald if you breed them too frequently. Most mini rex breeders I know just do a litter or 2 per doe in the spring and a litter or 2 per doe in the fall so they might only aim for 2 litters a year. The champagne d'argent doe got through 2 litters of 5 and then her 3rd litter turned out just to be a single kit and she's not being bred again until August. The creme d'argent x NZ doe insists on being bred constantly. She's a real pain when not bred because she spends all her time trying to get to the buck or humping the other rabbits. I bred her last fall and twice over the winter so I was gonna give her a break this spring but she was trying to tear through the divider between colonies to get to my champagne buck and being a real pain. I gave in and tossed my buck over there. She's stayed in good flesh and cared for her large litters with minimal issues so whatever she wants. I'm not actually sure which buck she's bred to right now because I left several of her half mini rex sons in that colony past breeding age since I didn't get around to butchering them while we were moving. She stopped humping and harassing the other rabbits about 2weeks ago so I'm assuming around then is when she got bred. I finally got nearly all of them butchered except one extra doe and I only kept one buck which I pulled out to a cage. I wasn't planning on breeding her again until august but if she holds condition and proves to be too much of a pest I'll put him back in after she has a few weeks break. The other doe in there should be old enough for her first litter by then too.