Study finds, on average, a dam that is 10% more inbred than another will produce one fewer puppy per litter.

New data has scientifically proved that inbreeding depression – the result of breeding closely related individuals – reduces litter sizes in pure-breed golden retrievers.

The study – conducted by Morris Animal Foundation research partners at Embark Veterinary in the US – was one of the first to examine genetic measures of inbreeding in domestic dogs, rather than using pedigree-based estimates.

Inbred influence

The data – published in the journal Mammalian Genome – is based on the Golden Retriever Lifetime Study (GRLS), which gathers information on more than 3,000 golden retrievers from across the US.

For the study, the team examined DNA and phenotype data from 93 female golden retrievers enrolled in the GRLS. All the dams were reproductively intact and had been bred at least once.

The team discovered the degree to which a dog was inbred influenced the number of puppies it birthed – on average, a dam that is 10% more inbred than another will produce one fewer puppy per litter.

Larger analyses

Erin Chu – senior veterinary geneticist at Embark, a dog DNA testing company based in Boston, Massachusetts – was reported in ScienceDaily as saying: “This scientifically proves something we’ve known anecdotally for a few years – fecundity, or the measure of how successfully a dog can reproduce, is threatened by inbreeding.”

Dr Chu said the work sets the stage for larger analyses to investigate genomic regions associated with fecundity and other measures of fitness, such as negative behavior, mortality and longevity.