Why do you say this? We have no idea how many mutations are present in different breeds. I sure don't and I'll bet you haven't a clue either.
Nor do you all have a clue about how many mutations, what kind of mutations, are needed to counter the trend to genetic reduction, nor whether they in fact play any role at all in any of the processes other than bringing disease, or whether pre-existing alleles in the population could account for all of it or not, because you are not thinking along these lines and not testing for them. It's all assumption.
(I do know what at least one modern cat breed is a direct result of a mutation so the chances of there being none between different dog breeds isn't too large).
Prove it. Start a thread and prove that it was a mutation rather than a pre-existing allele or combination of alleles. I dare you.
You don't seem to understand that you don't get to make up "facts".
Imagine that. Clearly it is what evos are doing when they assume that mutation is all it takes to power evolution. NO EVIDENCE. Most mutations are deleterious. Nobody has yet tried to SHOW that the ridiculously few known useful mutations could possibly counter all the factors that reduce genetic diversity, you just assume that it does.