SM was undoubtedly around back in the 1960s, some breeders have recalled having cavaliers that they could not walk on a lead. Obviously a lot of mildly affected dogs would have remained undetected.
Cavaliers all over the world, whether show lines or puppy farm stock descend from the founding dogs, but they will not have all developed in the same way.
Some countries were hard hit by SM a good few years before the UK, probably because particular imported UK dogs were used extensively at stud on the small population of resident cavaliers.
Other countries seem to have little SM in their home-bred stock although the use of unscanned UK imports will probably soon change that.
Puppy farm stock would be descended from the original founding dogs, but if they remained as a separate sub-population and the stud dogs used on them were not so line bred then they could offer different cavalier genes, and some of them may have less severe CM.
It is obviously wrong to draw conclusions from just one dog, and as I said this is just speculation on my part, but this thought was prompted by the fact that at the London Pet Show I was given the pedigree of a scanned ( at 4 years ) grade A dog where the the few names with affixes in the pedigree were well known PF names ( there were a couple of show champions in the fifth generation)
The owner had him scanned because her other dog had severe SM and she wanted to know whether he was also affected. He was KC registered and his COI was 1.3%
You are right Sins, it is a mess, one we got into unknowingly and no one is to blame for what happened originally, but that cannot still be said now.
This is not the researchers responsibility, or the KC or the BVA , it is the cavalier club members responsibility to bite the bullet,and however inconvenient, do what is necessary to breed away from the inherited problems in the breed and try and establish a nucleus of healthier cavaliers for the future.
There is a simple rule of thumb to indicate who is an irresponsible breeder even if it is not possible to check whether health tests have been done.
These days no responsible breeder should mate a dog or bitch younger than 2.5 years.....................So why is there at least one underage parent in half the litters registered by club members?
Cavaliers......Faith, The Ginger Tank and Woody.
Japanese Chins.... Dandy, Benny, Bridgette and Hana.
Remembered with love......... Tommy Tuppence and Fonzi