The Genetic Lottery – Do you want to play?

Frances O. Smith DVM PhD Diplomate ACT

Dog breeding is an art, a science and a game of chance – genetic chance. As breeders, we each set goals which we hope to obtain through the application of our knowledge of our breed, scientific and diagnostic modalities available to us and lastly through luck. We all know complete novices who have purchased a puppy from undistinguished parentage that goes on to an outstanding competition record in conformation, obedience or field events. We all also recognize that these animals are the result of chance and that the likelihood of success in any of the above venues is greatly enhanced when deliberate, thoughtful breedings are orchestrated.

Similar outcomes can be expected in the selection process used to produce a canine with an expectation of orthopedic soundness. Certainly, one can spin the wheel and hope to come out a winner orthopedically but as the odds would have it the odds favor the house (the random gene pool.) Improving your odds involves investigating the genetic background of your dog or dogs, applying diagnostic modalities as early as possible in the dog’s life and careful application of risk versus benefit decision making.

Recent data complied at the Orthopedic Foundation for Animals involving progeny testing yields some fascinating information. The data was compiled from 1994 through February 2003. This data involves 124,320 dogs who had radiographs of their pelvis submitted to the OFA for evaluation. Using information supplied by the owner regarding the sire and dam of these dogs a comparison was made to determine the percentage of dysplastic animals produced from these parents. In 117,391 dogs from normal to normal breedings, 9.3% of the progeny were dysplastic. In 2,576 dogs from a normal sire to a dysplastic dam, 18.8% of the progeny were dysplastic. In 4,068 dogs from a dysplastic sire to a normal dam 18.9% were dysplastic. In 285 dogs from a dysplastic sire bred to a dysplastic dam 33.7% were dysplastic.Thus your odds of obtaining a dysplastic dog are 3.62 times higher from a dysplastic to dysplastic breeding as from a normal to normal breeding.

Total number 124,320

Data from the same time period 1994 through February 2003 involves progeny testing comparing elbow status to known sire and dam elbow status. The statistics are as follows.

For 10,245 dogs from normal to normal breedings, 12.2% of the progeny were affected with elbow dysplasia. For 1,289 dogs from a normal sire to a dysplastic dam 26.1% of the progeny were affected. From a dysplastic sire to a normal dam, 31.3% of the progeny were affected with elbow dysplasia. From 272 dogs from a dysplastic sire bred to a dysplastic dam, 41.5% of the progeny were affected. Multiple conclusions can be reached in the analysis of this elbow data. Firstly, it is important to understand that elbow dysplasia includes, ununited anconeal process, ununited medial coronoid process, and osteochondrosis of the elbow joint singly or in combination resulting in degenerative joint disease of the elbow. It may be that elbow dysplasia has a higher heritability coefficient than the heritability coefficient for hip dysplasia. Alternatively, it may be that our phenotypic diagnostic test (radiograph) is less sensitive (results in more false negatives) than does our phenotypic test (radiograph) for hip dysplasia. From an odds standpoint, a breeder takes a far bigger chance of a negative outcome (an affected animal) by taking a chance on the offspring of a dog or bitch afflicted with elbow dysplasia than if they were risking the negative outcome of the offspring of a dog or bitch with hip dysplasia. The chances of an affected animal are 11/2 to 2 times higher in these breedings.

Total number 13,151

Numbers as dramatic as these give one pause when the genetic lottery is considered. Selection for phenotypic normal status greatly improves the breeder’s odds of normalcy (a win). Failure to select results in greatly increased odds of a disappointing outcome (elbow or hip dysplasia.) So, spin the wheel with the odds weighted in you favor – let’s help all the dogs to win...