Inbreeding and Longevity in Bernese Mountain Dogs Pat Long and Bert Klei PhD
Coefficient of Inbreeding (COI) Scientific: The probability that two alleles at a locus are identical by descent. Practical: The chance that the two copies of a chromosome in an animal are coming from the same ancestor. Practice: If the dam and the sire are related the resulting puppies will be inbred. The COI depends on the level of relationship between the sire and the dam.
Why do We Mate Relatives? It happened by accident. We did not know that animals were relatives. We cannot avoid it. It can happen by design.
Effects of Inbreeding • Reduced fertility • Increase in genetic disorders • Lower birth rates • Loss of immune system function • Lower growth rates • Reduced longevity • Standard Poodles 1% increase in inbreeding results in 1 month shorter life span (Armstrong, 2000)
Examples of Matings and Resulting COI Full Sib COI = 25% Parent – Off-Spring COI = 25% Half Sib COI = 12.5% Uncle – Niece COI = 12.5% First Cousins COI = 6.25%
Example 4 2 5 1 6 3 5 Individual 1 is the result of a half sib mating. We can draw a path from 1 2 5 3 1 5 is the common ancestor, or the ancestor to which we are line breeding. It took us 4 steps to get from 1 back to 1. COI(1) is ½(4-1)=0.125=12.5%
Let’s Add Two Generations Based on this information none of the new ancestors are related. The only path that can be drawn from 1 to 1 is through 5. COI(1)=12.5%
What Happens with One More Generation There is additional information in a data base. Male 25 is the father of 14 and 21, female 26 is the mother of 13, 18, and 24. We can draw paths from 1 to 1 through 5, and new ones through 25 and 26. This is pedigree information most people might not remember. COI(1)=13.28% Since the common ancestors occurred many generations ago the impact is small. COI(2)=COI(3)=0.78% It can add up if many common ancestors occur.
Real Life Pedigree Example 45 generations 774 ancestors 10 generations in which all ancestors are known COI=36%
Longevity In this context: Simply the number of days between a dog’s reported birth and an animal’s reported death regardless of the cause of death as reported to Berner Garde
BernerGarde • First information collected in the 1970s. • Official start 1984 • Named Berner Garde in 1993 • Incorporated in 1995 • Mission: Ensure a long and healthy lifespan for the breed through the collection and dissemination of genetic disease information for research purposes • At the end of 2008 • 58,638 animals • 6,033 with longevity information
Methods • Tabular method to calculate inbreeding (Emik and Terrill, 1949). • Linear models to determine the effect of inbreeding on longevity taking into account the effect of: • Birth Year • Sex • Pet vs Breeding Dog Status • Inbreeding
Data Used All individuals for calculating COI (~60,000) Individuals with at least 8 generations of complete ancestor information for determining the relationship between inbreeding and longevity (789 dogs).
Example Revisited • The more generations of ancestry information that are available the higher the estimate of the COI. • Estimates of COI based on a reduced number of generations are always underestimating the true COI.
Results Inbreeding(Only dogs with at least 8 completely known generations)
Average COI by Birth Year(at least 8 complete generations of pedigree information)
Selecting Data By restricting ourselves to dogs with 8 or more complete generations of ancestry information we selected data. Selecting data can affect the results of the analysis. Need to make sure that our selected longevity data is a representative sample of all the available longevity data.
Median Longevity by COI Class(at least 8 complete generations of pedigree information)
Methods • The longevity data is bi-modal • Split the data: • 79 dogs dying before 2 years of age. • 710 dogs dying after 2 years of age. • Analyze them in two separate analyses
ResultsOlder than 2 Years of Age Ave COI 17.8% For every 1% increase in inbreeding a dog lives on average 20.6days shorter (p=0.0007) Females live 147days longer than males (p=0.02) Breeding dogs live 134days longer than pets (p=0.05)
ResultsYounger than 2 years of age Ave COI 17.8% For every 1% increase in inbreeding a dog lives on average 9.2days shorter (p=0.05) No difference in males vs females No difference in pets vs breeding dogs
ConclusionsLongevity Median Longevity of Bernese Mountain Dogs is ~8 years. Median Longevity has slightly increased since 1984. The data shows a period of early death (< 2 years of age) followed by death occurring around median age.
ConclusionsInbreeding When determining inbreeding the number of complete generations of pedigree information is important. Average inbreeding in Bernese Mountain Dogs is between 15 and 20%. The trend in inbreeding shows a slight decrease.
ConclusionsInbreeding & Longevity • Inbreeding does affect the longevity of Bernese Mountain Dogs. • 1% inbreeding results on average in a loss of 20 days of longevity for dogs dying after 2 years of age. Nine days for those dying before 2 years of age. • Other results from the analysis. • Females tend to live longer than males. • Breeding dogs tend to live longer than pets.
Acknowledgements Berner Garde Board Gary Galunas Evan Klei All Berner owners who submitted data to Berner Garde.