At what age would it be apparent that a dog did not have a good topline? Is this something that would be obvious at the 6 -8wks to someone in the know or would it only show later in the developement? If Mum and Dad both have good toplines would the pups always inherit this?

Pups go through so many stages that it can be very difficult to tell. I know of several in my breed that were rejected at 6 weeks only to come back together at 7 weeks ;-) Each breed will also look right at different ages which is why you will get different people telling you to check them at different stages in the nest. Some will be right for the breed at 6 weeks, others 7, and even others much later. Confusing, isn't it? :-D

You are more likely to get good toplines from parents with good toplines, but nothing is guaranteed. You have to take into account all of the ancestors as well. :-)

How true this is LindyLou. Many years ago, a very famous breeder gave me this invaluable piece of advice 'When you mate a bitch, you must remember you are not just mating her to the dog, you are mating her to all the dogs ancestors as well'