Information from the Scientific Committee of the Nordic Kennel Union, NKU/VK, regarding pedigree-based versus DNA-based inbreeding estimates.
Inbreeding in dogs refers to the mating of individuals that are related, which will lead to an increase in homozygosity, i.e., that an individual inherits two identical copies of a gene, one from each parent. Inbreeding and genetic variation are two sides of the same coin. The level of inbreeding can be estimated using pedigree information or by DNA analysis, the latter often referred to as genomic inbreeding.
A pedigree based inbreeding estimate will only capture the inbreeding that has occurred in the generations included in the calculation, typically a few generations back. Pedigree-based calculations of inbreeding can, nevertheless, be very useful in practical breeding, for the purpose of breeding planning with respect to specific combinations. Regardless of the level of genetic variation in the breed or in an individual, the risk of disease and inbreeding depression in a specific litter will increase if the parents are closely related. Avoiding these high-risk combinations will also help to limit the rate of increased inbreeding in the population. However, to estimate the accumulated, total level of inbreeding in a breed, one must either use complete pedigrees, or DNA-based methods. Since the former can be difficult in practice due to lack of data, DNA analyses are often the best option.
In DNA-based analyses of genetic variation and inbreeding (genomic inbreeding), the dogs’ DNA is examined directly. Genomic inbreeding is estimated by examining whether the dog is homozygous, i.e., lack genetic variation, in a larger proportion of their genes compared to other dogs. The methods used for calculation of genomic inbreeding may vary between different commercial providers. Consequently, results for dogs tested by different test providers are not directly comparable and implementation of genomic inbreeding in breeding planning is not straightforward. For individual dogs, breeding recommendations related to genomic inbreeding are still lacking and are difficult to develop due to the lack of standardisation regarding definition and calculation. DNA-based inbreeding tools are currently useful primarily to monitor and compare breeds at the population level, to assess the degree of genetic variation in the breed. Higher levels of inbreeding are associated with increased risk, but there is currently not sufficient evidence to define “how much is too much”. However, based on the precautionary principle, actions to increase diversity should be seriously considered in breeds where the levels of inbreeding are high.
For more extensive information regarding pedigree-based versus DNA-based inbreeding estimates, please see the document below, developed by the Scientific Committee of the NKU.