Perhaps one of the most important considerations in sustainable pedigreed dog breeding today is “genetic diversity” which refers to the total number of genetic characteristics in the genetic makeup of a species. Why is genetic diversity important in dog breeds?
As a breed loses genetic diversity it increases its chances of negative breed specific traits (including health issues) becoming widespread throughout the breed and also decreases its ability to survive its environment. For example, if faced with an infectious viral outbreak, in a diverse genetic population some dogs may have the ability to survive but if most dogs in that population share the same genes the chances of dogs in that breed surviving decrease. Other symptoms of the lack of genetic diversity in a breed might be decreased litter sizes, poor sperm quality, thrifty puppies and an increase of inherited health conditions within a breed. In purebred dogs there has been a significant loss of genetic diversity which has resulted from breeding practices going back to Victorian times such as inbreeding, the selection of specialized traits (e.g. hunting, herding, speed, health) use of popular sires and in some breeds such as the Cavalier a small amount of Founder dogs.
According to Arnold Jacques, President of the Belgian Toy and Cavalier Club, Member of the Scientific Committee of the Belgian Kennel Club and President of “Cavaliers for Life” “genetic diversity is considered good at 100; between 70 and 100 it is considered ok; at between 50 to 70 the breed will start to have some problems and once it falls below 50 there will be big problems within the breed.” In Cavaliers specifically, from a study of 120,000 pedigrees of dogs from Holland, Belgium and France it was found that the breed’s genetic diversity averaged 80 which is not bad, compared to some other breeds. However, according to Mr. Jacques, a breed must be careful when genetic diversity is below 100 as it can drop very quickly, reaching the so-called “bottleneck effect”.
Genetic diversity should be a consideration when attempting to eliminate health disorders in any breed. To expect to fix problems, which developed over 50-100 years – overnight, is neither practical nor safe for the future well-being of the breed. Breeders have to balance keeping a diverse genetic base within the breed with trying to eliminate health problems. History has shown that in breeds that attempt to move too quickly to fix problems can end up with a new list of health issues due to the decrease in genetic diversity. In fact, it has been speculated that, in the Cavalier King Charles Spaniel, when breeders started to eliminate dogs and lines with eye issues this led to the increase in heart problems and the rise in Syringomyelia may have been due to the attempt to eliminate MVD in the breed.
Some ideas currently under consideration to increase genetic diversity in the Cavalier are:
- Encouraging the breeding of all 4 colors by changing the Standard (UK) to allow for some white markings on wholesalers and blanket markings on particulars.
- Using Estimated Breeding Values (EBVs) when choosing mates.
- Using chilled and frozen semen to breed to dogs in different geographic locations.
For further information the article Bad Genes, Babies and Bath Water by C.A. Sharpp is an excellent article which discusses some of the issues in balancing genetic health and genetic diversity.