Understanding COI
Coefficient of Inbreeding — Learn how COI is calculated and used in Staffordshire Bull Terrier breeding
Search Dog
Find any dog and calculate its COI on the dog's page
Testmating
Calculate COI for planned matings before breeding
Breed Statistics
View population-level COI data and trends
What is COI?
COI (Coefficient of Inbreeding) is a mathematical calculation based on Wright's formula that measures the probability of inheriting two copies of the same allele from an ancestor that appears on both sides of the pedigree.
SBTpedigree.com offers COI calculation on all registered dogs in the database. Simply visit any dog's page and click "Calculate COI" to get an automated calculation based on 8 generations. The testmating tool can also calculate planned mating COI for 3, 5, or 8 generations.
Example: A bitch mated with its grandfather will result in a COI of 12.5%.
Why Use COI in Breeding?
Breeders often use high COI matings to double up on desirable traits and qualities they prefer in their breeding program. However, it's crucial to understand that this also increases the risk of doubling up on negative qualities, including those that may not be immediately visible.
Benefits
Can help consolidate desirable traits and characteristics in a breeding line.
Risks
May also amplify undesirable traits and hidden genetic issues.
Acceptability
What constitutes an acceptable COI level varies by individual breeder and country regulations.
Important: Some countries have restrictions on how high COI can be. When such restrictions exist, ensure calculations are done using the country's official pedigree system where you plan to register litters.
How COI Calculation Works
SBTpedigree uses 8, 9, and 10 generations for registered dog COI analysis. For planned matings, the testmating tool offers 3, 5, and 8 generation COI choices so breeders can compare shorter official-style calculations with the existing 8-generation value. Different COI systems may use fewer generations, which can result in different values.
In SBTpedigree's COI calculation, the dog or planned puppy itself is generation 0. The parents are generation 1, grandparents are generation 2, and so on. This means a 5-generation testmating COI counts five generations starting with the parents.
Key Requirements for Accurate COI
- A dog with missing ancestors in its 8-generation pedigree will not produce an accurate COI calculation.
- The calculation requires complete pedigree information to trace all common ancestors.
- Both sire and dam must have complete pedigree data for meaningful results.
Note: The COI calculation was first launched on SBTpedigree.com in 2014 through a joint effort funded by donations from several users. In 2021, the COI system was rewritten to fit the new website but remains based on the same calculation: Wright's Coefficient of Inbreeding.
The Mathematics Behind COI
Inbreeding coefficients are calculated using specific mathematical formulas that account for the relationship between parents and their common ancestors.
Understanding Inbreeding Requirements
For a litter to be inbred, both sire and dam must have one or more dogs in common between their pedigrees. Even if one parent is highly inbred, if the other parent shares no common ancestors, the resulting puppies will have zero COI.
This scenario rarely occurs in purebred dog populations, as most breeds are founded on a relatively small number of foundation animals whose names appear repeatedly throughout pedigrees.
Advanced Calculation Formula
When common ancestors exist, their own inbreeding coefficients must be factored into the calculation:
P1 = Number of generations from one parent back to the common ancestor
P2 = Number of generations from the other parent back to the same ancestor
FA = The COI of the common ancestor
This formula shows that the more inbred an ancestor is, and the more frequently that ancestor appears behind both the sire and dam, the higher the resulting COI will be.
Why Multiple Generations Matter
Simply looking at 3, 4, or 5-generation pedigrees is insufficient. Dogs appearing in a 5-generation pedigree may have many ancestors in common that aren't immediately visible.
Population geneticists recommend calculating COIs to at least the tenth generation. This broader view provides breeders with a more accurate picture of the true inbreeding coefficient behind any dog or planned mating. Use our testmating feature to calculate COI for potential breeding pairs before mating.
Why this matters: In breeds with bottlenecking episodes in their history, or breeds that have never been very numerous, knowing the COI of ancestors becomes critically important. This is especially relevant today given the popularity of line-breeding, which is another form of inbreeding that results in cumulative increases in COIs over generations. Explore our ancestor lines and ancestor families pages to understand breed lineage better.
Understanding Your COI Results
COI is Based on Pedigree, Not DNA
One crucial point to remember: COI is calculated based on what appears on paper (pedigree records), not actual DNA analysis. Since COIs are calculated solely by examining names on a pedigree, they represent probabilities, not absolutes.
COI predicts the likelihood that any allele may have come from a particular ancestor, or the probability that an individual's genetic makeup comes from one or more specific ancestors. This increases the likelihood that the individual may be homozygous for certain traits.
Important to remember:
A COI is not a guarantee of future greatness, nor is it a warning of potential deleterious effects of inbreeding. It's a tool to help make informed breeding decisions.
COI Needs Context
No COI stands alone. A COI is only valuable when compared to the population as a whole. You cannot determine if a COI is "high" or "low" unless you know the norm, mean, median, or average COI for your particular breed. Check our breed statistics to see population-level COI data.
Additionally, only COIs calculated in an identical manner should be compared. COIs calculated on the same individual using different methods can result in very different values.
Comparing Different COI Systems
Today, many pedigree-generating software packages and COI calculators are available for dog breeders. Many pedigree websites (including this one) and even some official registries display COI percentages on dog pages. Explore our site statistics to see comprehensive breed data and COI trends.
Why COI Values May Differ
Different systems may produce different COI values for the same dog because:
- They may use different formulas for calculation
- They may calculate to different numbers of generations
- Some systems may not include ancestral COIs in their calculations
- Missing pedigree data affects accuracy differently across systems
Best Practice: When comparing COIs, always ask the webmaster or breed warden:
- What formula is used for calculations?
- What does each symbol in the formula mean?
- How many generations are included?
- Are ancestral COIs factored into the calculations?
This information is especially important when dealing with registries that have placed restrictions on breeders using their services or importing dogs based on COI thresholds.
Recommendation: Due to the wide variation in COI accuracy across different systems, COIs should not be used as the sole, or even a major, determining factor when deciding whether to proceed with a particular mating. Consider COI as one tool among many in your breeding decision toolkit.
Our COI Contributors
A huge thanks to the people mentioned below. You have all contributed to making the COI script available at SBTpedigree.com.
On behalf of all SBTpedigree.com users — Thank you for your contribution!
Article Source: chessieinfo.net