Enlarge and/or maintain genetic diversity
What is genetic diversity?
When looking at the people around you, you will notice many differences in for example skin colour, height and hair colour. That is what we call variation. The genetic differences between those people (partly) cause that exterior variation. In other words, we speak of genetic variation.
By genetic variation or diversity, the existence of differences (variation) in genetic material of a population is meant. That genetic diversity is responsible for the differences within a certain species and ensures that each individual is in fact unique.
Since variation determines adaptation, it is crucial to know how much variation there is within a population. The bigger the genetic diversity of a population, the better it can adapt to changing environmental factors such as epidemics, diseases, pollution and the climate.
Conversely, the lesser the diversity, the more uniform a population will be and the bigger the chance that it will not be able to adapt to new living conditions which in turn may lead to its extinction.
An animal which is the product of very close inbreeding, does not hold much genetic variation, even when it comes to its so-called health genes. Hence, it is more prone to all kinds of infections.
What causes the genetic diversity to drop?
One of the most important causes of the decreasing diversity is relying on inbreeding that is too close. Numerous breeds are the result of inbreeding, since it offers a chance to fix the wanted traits of a breed.
Another important cause is the frequent use of the same studs in a population, which in turn are related to one another. That is the so-called culture of champions. In theory, there is no limit to the number of descendants of a stud. The frequent use of the same stud will cause a drop in the diversity, but since that stud has many descendants, chances are that some of them will also be champions, which in turn will once again be frequently used and hence lead to a continuous drop in the genetic diversity of a population.
Excluding a large part of the population from breeding could also have an adverse effect on the genetic diversity of a population. For instance, that can happen when selecting against a certain affliction or toward a certain trait.
Most breeding rules set up by breed clubs contain one or more conditions that exclude some dogs from breeding. It can be said that those exclusion conditions are usually inefficient and have a negative influence on the diversity.
Hence, individual breeding exclusion is to be avoided at all costs. Some trainings (e.g. veterinary medicine, animal care and breeding) still advise against using affected animals and non-affected related animals for breeding. They do not take into account the effect of that advice on the health of the population and the next generation of animals.
What is meant by effective population size?
The effective population size is an important concept within genetics. A population of 10,000 dogs with an effective population size of 40 means that the genetic diversity of those 10,000 dogs corresponds to that of an ideal population of 40 dogs.
There is a connection between the increase in inbreeding throughout the years and the effective population size. A quicker rise in inbreeding is reflected by a smaller effective population size.
The minimal effective population size is 50, whereas a safe border is 100. The effective population size of a breed guarantees its long-term existence.
Breeders can select for any defects in a population, the effective size of which is more than 100. The selection criteria need to be loosened when the effective population size is between 50 and 100, since strict measures can cause the diversity to drop dramatically.
Any form of human selection is strongly discouraged in case of an effective population size less than 50, since fifty is the absolute minimum for a viable population.
However, even breeds with an effective population size of more than 100 suffer too many afflictions, the prevalence of which is too high in order to introduce an individual breeding restriction today.