Inbreeding has proven negative effects for health, says a new study in dogs

by Katariina Mäki

A recent study by an international team led by veterinary geneticist Danika Bannasch is a welcome wake-up call for all of us in the world of pedigree dogs.

While it has been well established that closed studbooks cause inbreeding to accumulate, the special importance of the study lies in the bond between inbreeding and health: the results in 162 breeds show that inbreeding contributes to an increase in disease and health care costs throughout the dogs’ life. Again, a known biological fact, but very important to once again have been proven also in dogs from an actual data.

A wide consensus based on studies in other animal species is that negative effects start to show when inbreeding level exceeds 10%. In the Bannasch et al. study, the accumulated average inbreeding based on genetic analysis across 227 breeds was close to 25 %, which is the level if mating together parent and offspring or full sibs.

Inbreeding levels in dog breeds have formerly been calculated mostly using pedigree data. It is however difficult to calculate the true coefficient of inbreeding (COI) from pedigrees unless the data reaches all generations – from the most recent ones to the founders of the breed. That’s what makes genotype-based methods so important. You can read more about the difference between pedigree COI and genomic COI in a DogWellNet Blog 'Ask Aimée' here.

Few studies based on complete pedigree information are available, one in Leonbergers by Letko et al. (2020), and another in Nova Scotia Duck Tolling Retrievers and Lancashire Heelers by Mäki (2010). Both studies reported levels of inbreeding similar to Bannasch et al.

Even more important than the level of inbreeding itself is the rate at which it has been reached. This rate defines the effective size of the population, which is a good indicator of the future viability of the population regarding inbreeding and genetic diversity.

To my knowledge, Bannasch et al. is the largest study showing the negative effects of inbreeding in dogs. The authors mention that demonstration of direct negative effects of inbreeding within breeds has been limited, one reason for this being the challenges of phenotyping for individual animals. They mention the studies by:

• Leroy et al. (2015): close inbreeding had a negative effect on litter size and neonatal survival in seven French dog breeds
• Chu et al. (2019): inbreeding was associated with smaller litters in Golden Retrievers and
• Schrack et al. (2017): inbreeding in dams was associated with fertility in the Entlebucher Mountain dog.
• Mäki et al. (2001) showed also that inbreeding was associated with dogs’ screening results in hip and elbow dysplasia. The association was found in the German Shepherd Dog and the Labrador Retriever, but it was quite weak, probably since the multifactorial nature of both dysplasias.

We know the situation – we have known it for a long time – how should we move forward? In any breed population, care should be taken to maintain genetic diversity. The Bannasch et al. study shows that most canine breeds are highly inbred, but some are still quite diverse, thanks to open studbooks or recent crosses.

We have tools to improve the situation in the breeds. These include:

• Use as many healthy dogs for breeding as possible
• Don’t overuse any dog
  • the so-called matador breeding creates unnecessary additional genetic bottlenecks and decreases variation. We must remember that every dog, even the best one, carries harmful mutations which spread all around in the population, if the dog is overly used for breeding.
• To avoid adverse effects of inbreeding in your own breedings, don’t combine close relatives – and remember that also linebreeding is inbreeding (See Brenda’s blog post, Linebreeding vs. Inbreeding – Let’s be perfectly clear.)
• In breeds where negative effects of inbreeding have started to show, or where it is simply difficult to find healthy dogs for breeding, consider using the old, formerly widely used tool – outcrosses. Planned, well-organized outcrossing is an efficient way to bring new genetic variation into population – a good way forward.

Inbreeding and genetic diversity is a challenge the International Partnership For Dogs will address in future work. Stay tuned!

References and links

Bannasch, D., Famula, T., Donner, J. et al. The effect of inbreeding, body size and morphology on health in dog breeds. Canine Genet Epidemiol 8, 12 (2021). https://doi.org/10.1186/s40575-021-00111-4

Bonnett B. Blog: Linebreeding vs. Inbreeding – Let’s be perfectly clear.

Chu ET, Simpson MJ, Diehl K, Page RL, Sams AJ, Boyko AR. Inbreeding depression causes reduced fecundity in Golden retrievers. Mamm Genome. 2019;30(5–6):166–72.

Leroy G, Phocas F, Hedan B, Verrier E, Rognon X. Inbreeding impact on litter size and survival in selected canine breeds. Vet J. 2015;203(1):74–8.

Letko A, Minor KM, Jagannathan V, Seefried FR, Mickelson JR, Oliehoek P, Drögemüller C. Genomic diversity and population structure of the Leonberger dog breed. Genet Sel Evol. 2020 Oct 14;52(1):61. doi: 10.1186/s12711-020-00581-3. Erratum in: Genet Sel Evol. 2020 Nov 18;52(1):70.

Llewellyn-Zaidi A. Blog: Ask Aimee: What's the difference between pedigree COI and genomic COI?

Mäki K. Population structure and genetic diversity of worldwide Nova Scotia duck tolling retriever and Lancashire heeler dog populations. J Anim Breed Genet. 2010;127(4):318–26.

Mäki K, Groen AF, Liinamo A-E, Ojala M. Population structure, inbreeding trend and their association with hip and elbow dysplasia in dogs. Anim Sci. 2001;73(2):217–228.

Schrack J, Dolf G, Reichler IM, Schelling C. Factors influencing litter size and puppy losses in the Entlebucher Mountain dog. Theriogenology. 2017;95:163–70.