Approved breeding guidelines and buying a puppy
At the request of many breeders, Dr Clare Rusbridge has for several years offered suggested breeding guidelines for minimising SM, revised as new information has become available. Initially, it was believed that breeders could focus on finding unaffected dogs and breed from those to rid the breed of this affliction -- those with neither the Chiari-like malformation (CM) of the skull that can cause SM, or SM itself. But unfortunately, every research sample, whether from North America, Britain or Europe, has shown the incidence of CM is far too high (in the region of 90% of cavaliers) and that SM rates are also disconcertingly high (the least-affected samples revealed that about 30% of dogs had syrinxes; while up to 70% had SM in one large sample that included many older cavaliers).
This forced a reconsideration, and in 2005 Dr Rusbridge introduced a grading system for dogs based on MRI results. She structured breeding guidelines around those grades, since refined and approved by all researchers at the 2006 London SM Conference (you can see the full breeding guidelines here), which try to balance the goal of striving for cavaliers with little or no CM/SM and the elimination of pain, against retaining as much genetic diversity in a breed already under genetic pressure. The gene pool in CKCS, a reconstructed breed, was always fairly small and, according to Dr Rusbridge, in the past 15 years much diversity has been lost due to a new tendency to (over)use a small number of champion sires ("popular sire syndrome"). Sires influence a breed's development and genetic heritage far more than dams because a dam might have at most, three to four litters over a lifetime, passing her genes to perhaps 20 puppies, while a top sire can father thousands of puppies that will themselves be bred, often to other descendants of that same sire. Unfortunately several of the past "popular sires" are known to have SM in their lines. According to Dr Rusbridge and her research partner Penny Knowler, "93% of top stud dogs in the UK are closely related to 1 or more dogs with SM and the pedigrees of these dogs are similar to Champions worldwide."
Therefore many researchers feel there is great urgency to MRI and find dogs that are least affected to bolster a genetic pool of possible breeding dogs that will be least likely to pass along severe SM. While the breeding guidelines have not been proven to work -- something that will take many years and further genetic work, such as that being undertaken in Canada as part of the genome project -- an initial, focused breeding scheme by Dutch breeders (reported at the London SM conference) and individual efforts worldwide are showing encouraging preliminary results. Researchers argue that the MVD breeding protocol, long accepted by breeders and backed by most CKCS clubs as a hallmark of good breeding practice, similarly remains unproven as such, but also received researcher backing over a decade ago and breeders using it report improved heart health and longevity.
The recommended SM breeding guidelines for cavaliers are included in this section of the website and can be found here.
Puppy buyer guide: looking for breeders following SM breeding protocols
Many puppy buyers are interested in finding breeders who follow the breeding guidelines, MRI their breeding dogs, and are using the least-affected or unaffected dogs try to breed away from syringomyelia. However, most buyers are not sure what certificates they should be looking for, or the questions they should be asking. To help puppy buyers, the SM Infosite now includes a new section with such a guide.
Buyers need to research the breeder and his/her lines, and look for appropriate evidence of the breeder's compliance with breeding protocols. This section explains what evidence a buyer should seek and the rationale behind the breeding guidelines, the MRI grading scheme, what a certificate will look like, and what to ask a breeder when looking for puppies.