Whew, big question. And this is fine as a question on breeding --
-- my issue is more on people asking for advice who are not focused on breed health and conformation but on making money off puppies or simply having some 'fun' breeding, disregarding the genetic havok they may cause by doing so in an uninformed way.
There is some ongoing statistical research at the moment to try and predict the probability of certain lines being carriers.
The concern with some of what is being done is that it has been dependent on 1) breeders being truthful about their scan results and 2) a consistency in how MRIs are being read. In the case of 1), I'd want every single piece of data to be based on an actual scan certificate that is verifiable, not on what people say. I do know what people say is the case was accepted as being the truth. In a research setting, that would make me concerned about the potential accuracy of the results. Regarding 2), one of the reasons the neurologists at the London SM conference last Nov chose to get rid of the A* (clear for the malformation, clear for SM) grade was because many felt there were some discrepencies in the grades some neurologists were assigning. Some are obviously better at reading MRIs and some are more familiar with SM/CM than others. I do know of several instances in which a couple of neurologists were giving total clears to dogs that other neurologists, having seen the scans, would have not have given an A* to. So ideally, the scans for such research should be read by a single individual or a group who review each scan, grade it, then come to a final grade decision. There is some proposed work intended to do just this, I believe; alternatively, the original statistical work needs to be published and subject to formal peer review.
All that said: it seems unlikely that many lines are free or even mostly clear for SM anyway and to remove all affected lines would decimate the genetic diversity needed to ensure the survival of the breed. So the focus at the moment is to look for A graded dogs (least or un-affected, no symptoms) via scanning and to work with breeders also scanning, and open about the pedigrees and health history behind that dog. A couple of years of scanning by Dutch breeders has provided some promising results showing that when an A graded dog is found there tend to be many other As amongst related dogs. Scanning IS showing this to be the case which implies that even in lines with SM, clusters of less affected dogs can be found and if used for breeding, should also produce mostly lesser-affected dogs. While no one knowns strictly that this would be the case, this is the entire basis of the MVD protocol which is similarly theoretical, but has proven results and is widely used by breeders. So far, no AxA mating has produced affected puppies, either.
You can read about this research in the paper presented at the London SM conference here
http://sm.cavaliertalk.com/research/london/london06.html
(paper Number 1):
The conclusions:
Both SM and MVD are known problems within the Dutch CKCS population that have reduced life expectancy from 13-15 years (for dogs of similar weight) to 8-10 years
Because SM has only been addressed on a consulting basis (eg when people have brought in an affected dog) it is impossible to make estimates of prevalence. However SM is expected to become more prevalent because asymptomatic cavaliers have been allowed to breed
Due to a private initiative from a Dutch breeder that started in 2002, 196 CKCS have been MRI-screened for SM. The point of screening is to identify the best possible breeding animals. Of these:
30% were graded A/B; 14% were C; 39% D, 13% E and 4% F, using the Rusbridge grading scheme. Overall 56% had SM. Blood samples were taken for all dogs for DNA research.
In a two year period, 2004-2006, Dutch breeders have increased the number of dogs scanning as A/B from 10% to about 25% by concentrating on screening relatives of clear dogs rather than random dogs
Early observations: 14 Breeders demonstrating best use of their clear dogs
Coping with large number of affected dogs
Initially A x D crosses predominated (not enough As)
Now A x A mating is an option
Up to 4 generations “SM clear”
SM Clear dogs related to other SM clear dogs
No SM affected dogs from A x A crosses
It is also worth getting a copy of Clare Rusbridge's thesis which goes into this in more detail. Penny Knowler has these for a donation to research:
[email protected]
It is worth PMing Nicki as well on this site, as she is in contact with a number of UK breeders who are scanning and working with the breeding recommendations and they can give far more hands-on, informed replies than me.
The breeding recommendations DO take into account the need to retain positive qualities in dogs other than A-grade dogs -- hence A grades can be bred to some other grades; the idea is to conserve as many good genes as possible while also working to reduce incidence.
BTW even the lines that have a lower statistical probability for producing SM-affected dogs CAN produce SM affected dogs -- as I own an affected dog from exactly those lines predicted in the casual research to have lowest incidence right now. But the exact same thing happens with MVD -- the goal with the MVD protocol as with the SM recommendations is to lower the overall probability of any dog getting the condition and reduce the severity when it does occur and to push back onset as in bioth cases, early onset of the condition tends to mean more severe forms of it. The best recommendation I think at present is to scan, know what you are breeding with on all sides, and use those dogs that have good general qualities but also are only mildly affected, if affected at all, by SM (eg as many A grade dogs as possible). Note mildly affected still means *asymptomatic*, not mildly symptomatic.
Hope that helps; if you are interested in further contacts Penny Knowler can likely provide some; Nicki knows many individual breeders as well.
