The real question is if the bitch is worth breeding back to back. Given the caliber of dogs you and I are generally discussing that's not an issue but just a general thought. There's a lot of crap out there that gets bred.
I have had back to back litters and reckon it's perfectly safe if not preferable given the right bitch. Some bitches really struggle through lactation and come out a bit rough. I wouldn't breed that kind of bitch back to back.
The bitch I have with the current litter is in better nic than at the mating and is still very active. I wouldn't hesitate to put her back in pup but my stud dogs are busy so there are plenty of good pups coming so another litter would just flood the market and outnumber the good homes available. NZ/OZ is a relatively small market. With the service dog program I was involved with in the US it was standard practice to breed 2 litters back to back then give the bitch a year off.
I have read plenty from sources I trust to convince me that given the right conditions, it is actually preferable to breed back to back. The conditions being that there is demand for pups, the bitch is in good condition and the right studs are available.
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