Australian Shepherd Health & Genetics Institute

Australian Shepherd Health & Genetics Institute

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Coefficient of Inbreeding


What is the coefficient of inbreeding (COI)?

COI is a measure of the common relationship between the two sides of a pedigree. Specifically, it is the measure of how likely any particular gene is to be homozygous (two like copies of the gene) by descent.  In other words:  The odds that a gene will have two copies coming down each side of the pedigree from the same ancestral source.

 Isn’t COI just a theory? 

Coefficient of inbreeding (COI) isn’t a theory, it’s a mathematical calculation.  It isn’t about “good” genes and “bad” genes, it’s a measure of how likely any given gene is to be homozygous (two like copies.)  A COI calculation is run over a set number of generations.  10 works for most breeds.

Why 10 generations?

COIs tend to rise with each additional generation. 10 is usually where the increase per generation flattens out so carrying it back further won’t provide any significant difference for the vas majority of dogs in the breed.

Why is COI important?

High COIs are associated with inbreeding depression, typified by higher frequency of disease and an increase in infertility and other reproductive failures.

Can we run COIs just on what we have on a printed pedigree?

Not for a useful result.  It is very possible to find two dogs that have few or no common names in these pedigrees.  This might look like an outcross, but they may be quite related if you go back a few additional generations.

What is the average COI for Aussies?

About 12.5%

 Should I make low COIs my primary breeding goal?

No.  You are breeding dogs, not numbers.  COI is a tool that helps the breeder monitor levels of inbreeding in her dogs.

What’s the best way to use COIs when making breeding decisions?

Strive not to exceed the average of the two parent’s COIs.  Try to stay below breed average if possible.  If a dog has a COI that is above breed average, give priority to matings that would produce puppies that are below average or at least 10% lower than the COI of the above average parent.  If both parents are over average, try t be 10% lower than the parent with the lower COI.   (Example:  Parents’ COIs are 25% and 20%, litter not to exceed 18%).  These considerations should be in concert with your evaluation of the virtues, faults and family health history of the dogs under consideration.

Does low COI mean that risk for disease is low? 

No. The coefficient of inbreeding (COI) is only a measure of the level of inbreeding a particular dog or cross might have.  It is not, all by itself, a predictor for any specific trait.  However, the closer the breeding, and therefore the higher the COI, the more likely you are to produce any trait, good or bad, known to occur in that line.  That is the reason people linebreed, the hope of concentrating genes for the traits they want to perpetuate.

However, if a line has health problem or any other unwanted trait, tight breeding increases the risk you will produce that disease.  On the other hand, you can do a breeding with 0% COI, say a Labrador to a German Shepherd Dog who both had hip dysplasia prominent in their pedigrees, you would increase risk for HD even though the COI was zero.