Health Corner: New and Old Approaches to Dog Breeding and Genetics

Health corner: New & Old Approaches to Dog Breeding and Genetics’ -Seminar by Dr. Sheila Schmutz & Dr. Joe Schmutz

By Sharon K. Schaefer
I was very lucky to attend this one day presentation by a couple, one of whom is a practising livestock/canine genetic researcher (Sheila) and the other a biologist, who are also breeders for 30 years of the rare Large Munsterlander hunting dog. Their combined practical experience and up-to-date DNA/genetic knowledge was wonderful. Early in the day we did a group exercise - we created imaginary matings for three different purposes using fictional dogs with known genetic problems in their 3-generation pedigrees.

One person there wouldn’t have used any of the dogs presented (they did not have a rare breed!) Both Sheila and Joe tried to impress on us the responsibility we have to not only produce nice puppies for our own breeding program but also to consider the risk/benefit to our breed as a whole. “Our dogs have a past and we can’t escape that, and our dogs have a future which we will help shape”. Breed tradition deserves respect - this is not a mousetrap we’re producing! When they get inquiries for brown Munsterlanders (breed standard calls for black) they refer people to breeders of Small Munsterlanders, when they get inquiries for shorter haired Munsterlanders they refer people to German Short Hair Pointers instead of trying to be all things to all hunters (and they never sell to non-hunters).

In this exercise we began to look at incidence, burden, and heritability of the traits and to see why for different breeds and different purposes, different decisions would be made. Incidence is the frequency with which a condition occurs. If you have 100 dogs registered and one of them has missing teeth that is a low incidence and you can choose to not breed that dog (and maybe parents, sibs).

If 50 or 80 of the 100 dogs have missing teeth then decisions have to change and you need to look at other factors. Missing teeth is considered a “low burden” because the dog can live a normal comfortable life at no extra cost to the owner but missing premolars is less serious (fully eligible to breed in their breed) than extra or missing incisors, canines or molars. Missing or extra premolars is an autosomal recessive trait so two carriers would give a 25% occurrence – the heritability of that trait (also classified as low, medium, or high). The inheritance of other teeth is unknown. They would consider missing canines a ‘breed with caution’ in their breed which means the condition should appear only once in a 3-generation pedigree. In another breed this might be impossible to achieve.

The majority of conformation and health issues are multi-factorial (used to be called polygenic) involving at least three different gene locations and environmental influences. It is difficult to identify the genes involved and even more difficult to eradicate the condition. The classic example of this is hip dysplasia. At the international genetics conference held in 2006, each of the three groups (Norberg Angle, OFA, and PennHIP) reported that researchers had mapped to three to four chromosomes involved in HD. This is a wonderful development BUT there was no overlap among the various chromosomes discovered so they cannot focus their work on one or two most promising locations. However since OFA judges bone conformation and PennHIP judges the looseness of tendons and ligaments the expectation should be that there will be several unique gene combinations involved.

Another point to research is the diversity and size of the original gene pool of your breed as well as its history to this point in time. Generally, breeds that were not inbred historically cannot handle inbreeding - it will not be a successful breeding plan. Breeds which began with a very small pool or which have gone through inbreeding and survived generally can be inbred successfully. We looked at calculating the coefficient of inbreeding using Wright’s Formula. When it came to colour genetics the information was overwhelming - I refer you to the website which is very readable and has been updated even since this seminar.

The internet is the primary educational choice because of the speed with which discoveries are being made in all genetic fields. Listed below are Sheila’s ‘colour genetics’ site and another recommended site for canine disease. However they caution us to take any information with a grain of salt, as what is true in one breed may not be true in another. For example, the eye disease Progressive Retinal Atrophy is an X-linked recessive in Samoyeds and Siberian Huskies but an autosomal recessive in several other breeds. Their favourite book reference [ed.: Lowell Ackerman’s The Genetic Connection] is preferred because it is a correct and cautious one.

Suggested references
Ackerman, Lowell The Genetic Connection: A guide to health problems in purebred dogs 1999. AAHA Press, Lakewood, Coloradohttp://homepage.usask.ca/~schmutz/dogcolors.htmlhttp://www.vet.cam.ac.uk/idid