In canine genetics, the COI (Coefficient of Inbreeding) is a concept that appears often, yet its purpose is frequently misunderstood. COI does not determine whether a mating is good or bad, nor does it predict a dog’s health or quality on its own. Instead, it serves as a descriptive measure that helps explain how a pedigree is structured.

What Is COI?

The Coefficient of Inbreeding (COI) is a calculation that reflects the probability that a puppy will inherit two identical copies of the same gene because its ancestors overlap. A low COI indicates fewer repeated ancestors in the generations analyzed, while a higher COI indicates more repetition. This does not imply anything positive or negative; it simply describes the genetic pattern of the pedigree.
 

What Is COI Used For?

COI helps breeders and owners:

• understand the genetic composition of a mating;

• compare pedigrees in a statistical way;

• identify trends within certain lines;

• evaluate the level of genetic diversity within a lineage.

 

By itself, COI does not determine the outcome of a litter. Rather, it provides context that can support thoughtful decision-making.
 

COI and Knowledge of Bloodlines: Two Complementary Tools

In practical breeding, COI is usually paired with another essential factor: knowledge of the bloodlines. Understanding the history of the dogs within a pedigree: what they have produced, the type they consolidate, how they have matched in previous combinations, and what strengths or weaknesses they may carry, is equally, if not more, important than the COI figure. A mating with a low COI may combine lines that are very different from one another, while a mating with a higher COI may be based on dogs that have consistently complemented each other over time. In either case, the result depends on the combination as a whole: structure, temperament, health, production record, and the breeder’s goals.
 

COI offers the mathematical perspective; knowledge of the lines provides the interpretive one.

 

An Indicator, Not a Prediction

COI does not evaluate health, structure, temperament, or compatibility between lines. Nor does it predict the success of a mating. It is simply a tool that describes the level of genetic repetition within a pedigree. How this information is used depends entirely on the breeder’s experience and approach.

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What Does This Mean for Someone Looking for a Puppy?

For someone searching for a puppy, COI can indicate that a breeder works with transparency and analysis, but it is not a decisive factor on its own. It is far more important that the breeder understands the pedigree, knows the dogs behind it, follows appropriate health testing, and selects combinations with logic and consistency.

 

COI complements this information, but it does not replace it.