This article by David Appleby (looks at a number of studies) says that six weeks is the best time for pups to go to their new homes:

http://www.apbc.org.uk/articles/puppysocialisation1

Taken from above:

"What practical applications do we have that bear out the research? Guide Dogs for the Blind, who, until 1956, used to rely on the donation of adult dogs which they took on approval to maintain their training stock. The success rate of these dogs fluctuated between 9 and 11 percent and it was recognised that this could be improved if the association could supervise the rearing of puppies. These were purchased and placed in private homes at between ten and twelve weeks old or even later. Things improved, but the results were not good enough. It was Derek Freeman, who pushed to have puppies placed in private homes at an earlier age to optimise socialisation and habituation during the critical development period. Derek had a strong belief in Scott and Fuller’s work and importance of early socialisation and habituation in the production of dogs that were best able to survive and perform in the world at large.

Derek found that six weeks was the best time to place puppies in private homes; any later critically reduced the time left before the puppies reached twelve weeks; but if puppies were removed from their dam and litter mates before six weeks they missed the opportunity to be properly socialised with their own kind, which resulted in inept interactions with other dogs in later life. The training success rate soared because of this policy, which was carried out in conjunction with the management of the gene pool via the breeding scheme Derek also pioneered. Annual success rates in excess of 75 percent became common. You might think that this is a special scheme for dogs with a special function. In fact, what the scheme provides is adult dogs with sound temperaments."

Part Two tells you how to socialise puppies:

http://www.apbc.org.uk/articles/puppysocialisation2

Sue

Interesting Kita. Must say I was surprised around 7yrs ago when I first moved here to find that they let the pups go by the time they are 6 weeks. Just because it was something I'd not been used to hearing about. But they do. And no one finds it at all surprising.

There isn't a solid reason for her to keep them that long, it's just what she is deciding to do for her own sake. All the stuff she told you seems to be more random than anything else IMO.

Mind you, I'm not a breeder... and I don't know a lot about this type of stuff. I do know that it's pretty unheard of around these parts for puppies to be deliberately kept until 12 weeks or more.

P.S.

A different strain of Lepto? Lepto has many strains and the one she is vaccinating against is simply not the same as the one your vet will vaccinate against. Who knows, the puppy might be more susceptible to the strain your vet vaccinates against. She just seems to be clinging onto the puppies... just my opinion.

I've done this on more than one occasion for various reasons, and my puppies are big puppies, and I have had as many as 12, just because you have never heard of it doesn't mean it hasn't happened.
A responsible breeder ensures that the puppies are going to the right homes (and even after unceasing effort it doesn't always turn out right) and that they also go with any requisite health tests, and if that means they stay with me longer, then that is what happens

All right. Good for you then! Do what you feel is right. Who am I to step in tell you otherwise? I don't breed dogs, and never, ever will so there it goes.

I've read that article before but got to say I disagree with that bit.
First of all, there's no links or actual citations of those studies. There's no explanation how Derek Freeman 'found' that six weeks is the best period to take puppies away from their mother. I've tried to find that article but couldn't.

Puppies have clear vision only at the end of week 5, you can't seriously say that within a few days they get to see enough of their littermates so that they're socially well equipped to interact with dogs in the future in a confident way. So if a puppy goes to a new home when it's 6 weeks old, the new owners would have to extensively socialise it with other dogs for prolongued periods of time for the puppy to learn to speak dog. Social interactions in dogs are so complex that it's impossible to learn from a few encounters with dogs they don't know. There's also a risk to overwhelm the puppy with new information while doing this. While if the puppy stays with the littermates for longer, it learns dog language in a completely natural way, from it's family.

The socialisation period doesn't end by week 12, but it's more optimal beforehand. But in my opinion it is the breeder's job to ensure enough socialisation and habituation has been done with puppies they've reared. Also, there's conflicting studies about the development of puppies. Some say that they start the fearful phase between week 6 and 8, so if you take a puppy away from it's mother when it's 6 weeks old, and it enters the fearful phase, you're already setting it up for failure.

John Bradshaw says in 'In Defense of Dogs' that at 8 weeks, puppies are in the middle of the 'sensitive' phase and taking them out of their environment at that age and putting them into a completely new situation could stress them out enormously.

So while I agree with parts of David Appleby's article but not with the part where he cited Derek Freeman's study and conclusion that puppies are best homed when 6 weeks old.
The second part of the article explains how to socialise puppies doesn't really take into account socialisation with other dogs. It mainly talks about other people, children, places, household equipment etc. and only at the end and only briefly talks about socialisation with other dogs and there he merely says 'go to puppy classes'. Considering that he's advocating homing puppies at 6 weeks, before they've properly been socialised with their own species, he's really not taking much notice of the imminent necessity of socialisation with other dogs.

I find this quite worrying because most behavioural issues with dogs that aren't training issues, are dog-dog problems. Considering that most of those dogs haven't been properly socialised after leaving the litter and add to that the fact that reputable associations like the APBC promote early homing before proper socialisation even with their littermates, and you get a whole new generation of problem dogs.

Just because something is 'unheard of' doesn't make it wrong.
Change needs to start somewhere..

I didn't say it was wrong. I don't think it's wrong. I think it's the breeder's personal choice. It's only a few more weeks, it's easy to just wait anyway. It's not 20 years.

I don't breed and don't know a lot about it... so I don't have a solid opinion anyway. For reference, are you suggesting that ALL breeders should keep puppies that long?

I really don't see the need for that in all situations, but it's the breeders personal choice regardless. It's not a huge deal IMO, but again... I'm not a breeder and know little about this type of stuff.

The longest I've ever waited for a puppy was nine weeks and that was my choice because we were going on holiday beforehand. I can honestly say that dog was the worst I've ever had for dog on dog problems but that could just have been her - I don't think you can generalise. The youngest I've ever had a puppy was five and a half weeks and I didn't realise how young he was until I received his papers! He is my most sociable and friendly dog.

I would not be happy waiting twelve weeks knowing all the work I would have to do to catch up!

I would not take on a pup at 12 weeks.