Humans began the development of domesticated dog breeds, tens of thousands of years ago. These dog breeds were developed with certain favourable physical and behavioural characteristics in mind. Breeding for these favourable traits has resulted in “pure-bred” animals with identifiable breed characteristics. 

This practice is known as linebreeding, which is a form of inbreeding. Inbreeding and linebreeding can be quite a controversial topic, especially in the canine breeding world. The difference between the two is not all that different, even though inbreeding is seen as something taboo, and linebreeding is considered an accepted practice. Understanding the risks of each practice can be an important decision-making tool for breeders.

Inbreeding is described as the mating of closely related individuals who have one or more common ancestors, whereas linebreeding is where the mated pairs are still related, but these mating pairs do not include first- or second-degree relatives. To explain in more detail, first-degree relatives share at least half of their genetic material, and includes parents, children, and siblings, whereas second-degree relatives only share a quarter of their genetic material, and this will include grandparents, half-siblings, and aunts or uncles.

While the concept seems straightforward, inbreeding can have several complex implications, impacting everything from deleterious recessive traits to having potential benefits in specific environments. This complex interaction of genetics and ecology makes the study of inbreeding crucial in both conservation and breeding practices.  

In nature, inbreeding can happen due to limited population sizes, habitat fragmentation, or social structures that limit mating choices. In captivity, such as amongst a population in a zoo or in domestic breeding programs, inbreeding may result from controlled breeding practices aimed at maintaining specific traits, resulting in a limited genetic pool. This limited gene pool amongst a population leads to inbreeding depression - the negative impact that comes as a result of breeding individuals that are related. Inbreeding depression can include genetic health problems in dogs, as well as a decrease in lifespan, fertility rates, immunity to diseases, and litter sizes. There have also been cases of physical aspects as such dogs having overbites, being smaller sizes and having behavioural problems. Common breed specific problems, like hip dysplasia in German Shepherds, are due to repeated inbreeding early in the breeds’ lineage which now have become accepted characteristics of these breeds. Breeders can counteract these effects by introducing new genes through importing stud animals or semen from different breed lines.

Achieving pure-bred animals often involves line breeding, allowing desirable attributes to be increased within a line. It is also common for certain genetic traits to quickly become diluted throughout the generations after they are introduced, whereas linebreeding counteracts this. Linebreeding dogs may be used to acquire a certain characteristic and then maintains uniformity throughout generations. In this way, the homozygosity (those traits that require two copies of a recessive allele to present itself physically) is increased, which may ensure lower health risks and increased energy in these dogs. 

While effective in keeping certain desirable traits within their lines, the line-breeding technique can reduce gene variability, leading to potential health problems. Those health problems get passed on through the generations till it also becomes an accepted trait. However, this is to the detriment of the animal and to the breed as a whole. Inbreeding depression may not be immediately visible in your lines. It will start with small issues, like a single puppy with an overbite, or a few dogs suddenly developing cataracts at a young age. Eventually over the generations these lines will not be able to continue either due to health issues or fertility issues. 

If done irresponsibly, linebreeding affects not only individual health but also the long-term survival and adaptability of populations. This means that the lack of genetic variation caused by extreme inbreeding may lead to the extinction of the breed. 

As a responsible breeder, it is important that you monitor your lines and consider bringing in new genetics from an outside source. Testing your breeding dogs for known recessive conditions, especially those that are common within that breed, is also important to ensure healthy lines. Regulatory bodies can potentially assist breeders with calculating breeding coefficients, which helps with making informed decisions about mating pairs. If you have dogs who are carriers for a recessive condition, breeding carriers with clear animals is safe, but carriers should not be bred with each other as this increases the risk of producing affected offspring. By continually breeding with clear animals, the recessive gene can eventually be eliminated from the population, improving the breed's genetic health over time. Through informed breeding practices and genetic management, the negative impacts of inbreeding can be minimised, guaranteeing the sustainability of the various canine breeds.

Where can I get genetic health tests done? 

At ZooOmics, we provide both health and colour testing as well as DNA profiles for both canine and feline. We utilise innovative technology to perform mutation testing and provide certificates for all testing, which can be submitted to registrars and breed societies. 

For inquiries about sample collection, shipping, processing, and services, please contact us at info@ZooOmics.co.za. Alternatively, visit our website at www.zooomics.co.za to download our sample submission form.