Friday, October 25, 2019

The importance of interpreting published work in an unbiased manner.




Recently  (22 August 2019) Dr. Tamas Jakkel of the Federation Cynologique Internationale (FCI) gave a talk “Preserving breeds, debunking myths”. (available on their FB page) In it he referred to a publication that he claimed showed that pedigree dogs are healthier than mixed dogs. In reality the exact opposite was true if anyone looks at the original publication. The publication did find that mixed dogs have more gDNA alleles that are associated with known health issues. This can be expected since the mixed dog may well pick up such a gene from both parents who may have different issues. However what he did not say or recognise or at worst deliberately hid was that the mixed dogs were nonetheless healthy because they only had one copy of these mutant genes so were “carriers” rather than “at risk”.

There have also been talks given and blogs written giving as an example that while boxers have the highest numbers of dogs “at risk” for DM they are not the highest to develop DM. There is of course a simple reason if we look a little bit deeper. DM effects dogs as they mature and sadly many boxers simply die too early for DM to show up. "With a median life span of 10.5 years and an expected range of 9 to 12 years, one does not expect a Boxer dog to live far into his teens. Reasons for this include the quite high cancer rates with this breed and heart issues. "  You can find the factual explanation and link to the actual publication here. https://www.instituteofcaninebiology.org/blog/why-do-mixed-breed-dogs-have-so-many-mutations?fbclid=IwAR0TnE_0x7btOwYfS1PFY57W7P6gspw05Fp6bdFe3WXhyEovSvkjF8QfxOg

DM is a big problem in many dogs with Canaan pedigree dogs being among the most effected – certainly in the USA. I have yet to see figures for Canaan dogs in Europe but do know that a number of breeders have experienced this problem.  We have to remember that being at risk ie. 2 copies of the gene,  to quote Embark DNA testing (run by Boyko of Cornell University), “Testing positive is predictive of your dog being affected by this condition, but it is not a final diagnosis nor does it predict when symptoms may occur or the severity of a condition in your dog.”  DM has no cure and is a nasty way for a dog to die so breeders really need to avoid producing at risk dogs. We also need to realise that having only one copy nor indeed none, of some of these health  issues does not mean a dog may not develop a problem since outside factors also have a role to play.

The ONLY way to know the health status of a dog to be used for breeding is to have it tested and not only for issues known to exist but for all, unless of course both parents are known to have been affected, or all dogs in a breed have been previously tested clear. For most breeds of dogs breeders have to work around this. Simply not using any dog with any of the known genetic health problems could lead to the loss of other valuable (to breeders) genes.  So what to do?

If a dog is at risk (2 copies) if bred with a dog known to be clear (0 copies) then ALL the pups will be carriers, fine if they are never bred but important to know if down the line an owner decides to breed. If an at risk dog is bred with a carrier (1 copy) then for each individual puppy born there is a 50/50 chance it will be at risk or a carrier. It is possible all will be at risk or all will be carriers. Not worth the risk.

If a both dogs bred are carriers (1 copy of the gene) then each pup may have a 25% chance of being clear, a 50% chance of being a carrier, or a 25% chance of being at risk. Yes once more it is possible all will be clear, all will be carriers or all will be at risk. There is no way to predict.  Again not worth the gamble if we don’t want to be guilty of producing dogs that will suffer.

If a dog that is a carrier is bred to a dog that is clear then each pup has a 50/50 chance of being clear or a carrier. Again not a problem but needs to be understood and tested if used for breeding.

For most breeds that’s about all that can be done without some form of out breeding.

In the case of the Canaan pedigree dog there remains a chance of bringing in more freeborn dogs, however it is vital that in doing so they should be genetically tested FIRST and not used if they have any genetic health issue. Why go to the trouble and cost of bringing in more problems.  Embark them first!

Breeders also need to accept that the type of pariah dogs that were used to establish the human controlled breed are wide spread and plentiful as genetic evidence shows. Do they test as “Canaan dogs”? No of course not because the pedigree dogs come from little over 30 from a relatively small area, with a few added more recently, so are all now more closely related and we cannot expect  to find those close relatives in the wild, although not impossible. Some of these dogs end up in shelters where they are invariably neutered but if the desire to preserve an ancient type was properly explained I believe there could be co-operation set up to introduce some to the pedigree breeders. This is a unique opportunity for Canaan breeders and could even be used if handled properly in the long term to total phase out even carriers of DM and other genetic issues.

Genetic health issues in free born  “village dogs” versus “Canaan dogs”.




Looking at a greater number of these freeborn dogs than was used to establish the Canaan pedigree breed, none of these dogs were at risk for any of the genetic health problems tested by Embark.

9 of 47 (19%) dogs carried one copy of the allele coding for Degenerative Myelopathy (DM) so 81% were normal. The Orthopaedic Foundation for Animals (OFA) in USA figures for 1918 show Canaan dogs, a pedigree breed established in the 1930s from village dogs show an alarming rate of 6.4% abnormal (at risk) for DM with 38.2% carriers with only 55.4% normal. Compared to other breeds Canaan dogs ranked a high 22nd. No figures were available for Canaan dogs in Europe but it is known that DM has been a problem in them.


Canaan dogs
Village dogs
Degenerative Myelopathy


At risk
6.40%
0%
Carrier
38.20%
19%
Clear
55.40%
81%





Choroidal hypoplasia, (Collie eye anomaly) was carried by 2 “village dogs”. These 2 dogs from Umm al Quwain, UAE were closely related, sharing 40% of their DNA (half siblings). This does not seem to have been reported in Canaan dogs but surely any new freeborn dogs added should be tested for all known health issues so as not to inadvertently create a problem.

von Willebrand type 1 a bleeding disorder was carried in 1 dog from Sohar, Oman with 1 copy of the allele. Again a reason to fully test all new freeborn dogs before adding them to the pedigree Canaan dogs.

Low normal ALT 25 of 47 dogs (53%) had one copy of the allele coding for low normal ALT and 1 had 2 copies. This does not effect the health of dogs but is important to know since a dog having this, when suspected of having liver problems, could give an ALT result generally considered normal but could in fact be raised for that dog. With a high percentage of this being present at a carrier level. Without testing pedigree Canaan dogs we simply do not know if it is present in the breed or not.




No comments:

Post a Comment

Note: Only a member of this blog may post a comment.