Understanding the difference between inbreeding and linebreeding

The distinction between inbreeding and linebreeding is often confusing. A common misconception is that successful outcomes are attributed to linebreeding, whereas failures are blamed on inbreeding. Another inaccurate belief is that inbreeding refers to sibling matings (for example brother and sister), whereas linebreeding involves parent-offspring pairings. In reality, both scenarios are incorrect and should never be pursued intentionally due to its potentially serious genetic consequences.

- By Dr Helena Theron, manager: genetic and professional advisory services, SA Stud Book

While avoiding inbreeding entirely can be challenging, especially in small populations, it is possible. For example, pedigrees of the South African Friesian horse trace back to the late 1800s, and despite being a relatively small population, breeders have successfully kept average inbreeding levels low through careful planning, selective breeding, and the strategic importation of animals.

Disadvantages of inbreeding

The true definition of inbreeding is the mating of closely related animals, such as brother x sister, parent x child, or nephew x niece. The disadvantages have been well documented and thoroughly researched. Inbreeding reduces variation within the population and can lead to the loss of valuable genes, since fewer unique ancestors are represented in an individual's pedigree.

The most serious drawback is inbreeding depression. This occurs when harmful genes, such as those associated with reduced fertility, poor survival rates or weakened immunity, are widespread in the population. Inbreeding therefore reduces genetic diversity and, in severe cases, contributes to the extinction of a breed or species.