MO- We take our babies (New Zealands) away from momma around 4.5 to 5 weeks- by this time they're usually just stressing the doe out and eating mostly on their own. Of course, I do leave the litter together and pay close attention to their diet but they're no longer on milk. My doe then gets rebred; usually within 2 weeks. Just take a look at them- at 3 years they've been producing like this since about 8 months (some breaks possibly) and are still in top condition. If condition lacks, does get a break. It all depends on the care of the animal.
Example: Dairy cows. In Florida, many large dairies are cement floored. The climate is already hot and humid and the cows are bred on the same schedule as here in PA. Here in PA, though, dairies are more "natural" and the cows are allowed to graze out in pasture during gestation AND lactation. Florida- likely to get 3 cycles. PA- likely to get 8. Care of the animal.
Also, tattooing is not inhumane in any way. Honestly, it's a couple seconds of stinging or vibrations and tada- permanent tatoo. A leg band? We used to band our birds and THAT was inhumane. Too many times you have to band young and later the band gets so tight it cuts off circulation or provides a wonderful habitat for mites- that's just great.
Sorry if this sounds like a strike out but the question asked was what CAN be- not what SHOULD be and I believe ethics should be avoided in most cases in this part of the forum simply because we do have breeders AND pet owners. So simply- a doe CAN be bred as soon as she has birth. A doe SHOULD be bred- whenever if at all- it's up to the owner.
That's my "I'm 35 weeks pregnant, huge, backache and tired of being hasseled" rant..