Learning Objectives

By the end of this module, you will be able to:

• Define the Coefficient of Inbreeding (COI) and explain what it measures.

• Understand how COI is calculated and what the percentage represents.

• Recognize the strengths and limitations of COI as a breeding tool.

• Differentiate between genetic relatedness and genetic quality.

• Use COI in conjunction with pedigree analysis, health testing, and breeder experience.

• Apply COI thoughtfully when planning Bedlington Terrier breedings.

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Introduction

Among today’s breeders, few topics generate more discussion—and more misunderstanding—than the Coefficient of Inbreeding (COI). Advances in pedigree databases and online breeding tools have made COI calculations readily available, leading many breeders to focus on a single percentage when evaluating potential matings. While COI is an extremely valuable tool, it is also one of the most commonly misinterpreted measurements in canine breeding.

Some breeders believe that the lower the COI, the healthier the puppies will be. Others dismiss COI entirely, believing it has little practical value. Neither view is correct.

Like every genetic tool, COI provides useful information, but it cannot answer every question. It does not measure health, quality, or the likelihood of producing champions. Instead, it estimates the probability that two copies of a gene in an offspring are identical because they were inherited from the same common ancestor. Understanding what COI can—and cannot—tell you is essential for making informed breeding decisions.

For preservation breeders, COI is best viewed as a guide rather than a rule. It helps estimate genetic diversity within a planned mating, but it should never replace thoughtful evaluation of the dogs themselves, their families, and their long-term contribution to the breed.

What Is the Coefficient of Inbreeding?

The Coefficient of Inbreeding, commonly abbreviated COI, is a statistical estimate of genetic relatedness.

More specifically, it measures the probability that a puppy inherits two identical copies of the same gene from a common ancestor.

This occurs because related dogs often carry identical copies of genes passed down through previous generations.

The closer two breeding dogs are related, the greater the chance they will pass identical genes to their offspring.

The result is expressed as a percentage.

For example:

• 0% COI indicates that, based on the available pedigree, no common ancestors appear within the generations analyzed.

• 10% COI indicates approximately a 10% probability that gene pairs are identical by descent.

• 25% COI is similar to what would be expected from a parent-to-offspring or full sibling mating.

It is important to remember that COI is a probability—not a direct measurement of DNA.

Why Does COI Matter?

Every dog carries both desirable and undesirable genes.

Most harmful recessive mutations remain hidden because they are paired with a normal copy inherited from the other parent.

As related dogs are bred together, the chance increases that offspring inherit identical copies of recessive genes from both parents.

Sometimes this produces exceptional consistency.

Sometimes it reveals inherited diseases.

More often, it does both.

This is why COI matters.

It helps breeders estimate the likelihood that genes—good and bad—will become homozygous in future generations.

Homozygosity: The Double-Edged Sword

The concept underlying COI is homozygosity.

A homozygous dog inherits the same version of a gene from both parents.

Greater homozygosity leads to greater predictability.

This is one reason linebred families often produce remarkably consistent puppies.

However, homozygosity does not distinguish between virtues and faults.

It can fix:

• Beautiful breed type

• Excellent movement

• Stable temperament

• Strong working ability

It can also fix:

• Copper Storage Disease mutations

• CDDY-associated variants

• Poor dentition

• Weak fronts

• Autoimmune tendencies

• Reduced fertility

Every increase in homozygosity carries both opportunity and risk.

What COI Does Not Measure

Perhaps the greatest misunderstanding is assuming COI measures quality.

It does not.

COI cannot predict:

• Intelligence

• Temperament

• Soundness

• Longevity

• Fertility

• Movement

• Show quality

• Performance ability

Two breedings may have identical COIs while producing dramatically different outcomes.

Why?

Because COI measures relatedness, not which genes are being shared.

Two outstanding dogs from healthy families may produce excellent puppies despite a moderate COI.

Conversely, two unrelated dogs with serious inherited problems may produce unhealthy puppies despite a very low COI.

Breeder’s Insight

COI tells you how closely related two dogs are—not whether they should be bred together.

The Myth of the “Perfect COI”

Many breeders ask:

“What is the ideal COI?”

The honest answer is:

There isn’t one.

No scientific study has identified a universal “safe” percentage applicable to every breed.

Why?

Because every breed has a unique history.

A 10% COI in one breed may represent excellent diversity.

The same percentage in another breed may reflect significant inbreeding.

The Bedlington Terrier has a relatively small worldwide breeding population compared to more numerous breeds.

Consequently, preservation breeders must interpret COI within the context of the breed’s history and available genetic diversity—not as an absolute number.

Low COI Does Not Mean Healthy

This is perhaps the most important lesson in this module.

A low COI simply means the parents are less closely related.

It says nothing about:

• Their health

• Their pedigree

• Their temperament

• Their structural quality

• Their reproductive success

Imagine breeding two unrelated dogs.

Both carry:

• Allergies

• Poor temperament

• Weak movement

• Low fertility

The resulting litter may have an exceptionally low COI.

It may also be disappointing in every other respect.

Low relatedness is not the same as genetic excellence.

High COI Does Not Automatically Mean Poor Quality

Likewise, a higher COI should not automatically eliminate a planned breeding.

Many influential preservation kennels have produced generations of outstanding dogs through careful linebreeding.

What mattered was not simply the COI.

What mattered was the quality and health of the family behind the pedigree.

High COI becomes concerning when accompanied by:

• Declining fertility

• Increasing inherited disease

• Reduced longevity

• Smaller litter sizes

• Poor immune function

• Loss of vigor

These changes represent inbreeding depression, not simply a high numerical COI.

COI and Inbreeding Depression

Inbreeding depression refers to the gradual decline in biological fitness that may occur when genetic diversity becomes too limited.

Possible signs include:

• Reduced fertility

• Smaller litters

• Increased puppy mortality

• Reduced lifespan

• Increased autoimmune disease

• Poor immune response

• Reduced reproductive performance

Not every highly linebred family experiences inbreeding depression.

Not every low-COI family avoids it.

This is why breeders monitor entire families over generations rather than relying on percentages alone.

COI Is Only One Piece of the Puzzle

Responsible breeders never make breeding decisions using COI alone.

Instead, they combine it with:

Health Testing

DNA tests, orthopedic evaluations, eye examinations, cardiac testing, and breed-specific screening help identify inherited health risks.

Pedigree Analysis

Pedigrees reveal patterns that no single dog can demonstrate.

Family History

Experienced breeders ask:

• How long did relatives live?

• Were there reproductive problems?

• Did autoimmune disease appear?

• Were certain structural faults common?

Temperament

Stable temperament remains one of the most heritable—and important—traits in the breed.

Structure and Function

A pedigree filled with healthy dogs is still incomplete if the dogs lack correct breed type or functional movement.

Longevity

Families that consistently produce healthy dogs living well into old age contribute tremendous value.

Reproductive Performance

Fertility, whelping ease, maternal instincts, and puppy survival all have important genetic components.

Using COI in a Bedlington Terrier Breeding Program

The Bedlington Terrier presents unique challenges.

As a numerically small breed, maintaining genetic diversity while preserving breed type requires careful planning.

Today’s breeders must also consider inherited conditions such as:

• Copper Storage Disease

• CDDY/IVDD

• Other emerging health concerns

Reducing disease risk should never come at the expense of eliminating valuable families unnecessarily.

COI helps breeders balance these competing priorities.

It should guide thoughtful decision-making—not dictate it.

Practical Questions Every Breeder Should Ask

Before planning a breeding, ask yourself:

• What is the COI?

• Why is it that number?

• Which ancestors contribute most heavily?

• What virtues are being concentrated?

• What faults may also become concentrated?

• Does this family demonstrate longevity?

• How is fertility?

• Are inherited diseases increasing or decreasing?

• Will this breeding preserve future options?

These questions are often more important than the percentage itself.

Case Study

Breeding A

COI: 3%

• Unrelated parents

• Weak temperaments

• Poor movement

• History of allergies

Breeding B

COI: 12%

• Healthy family

• Excellent longevity

• Strong breed type

• Extensive health testing

• Known carrier managed responsibly

Question:

Which breeding better serves the future of the breed?

The answer cannot be determined from COI alone.

Responsible breeders evaluate the entire genetic picture.

Key Takeaways

Remember these principles:

• COI estimates genetic relatedness—not quality.

• Lower is not automatically better.

• Higher is not automatically worse.

• COI should always be interpreted alongside health testing, pedigree analysis, and family history.

• Healthy breeding programs balance consistency with genetic diversity.

• Every breeding decision should consider the future of the breed—not simply the next litter.

Module Summary

The Coefficient of Inbreeding is one of the most valuable tools available to modern breeders, but it is only one tool among many. It provides insight into the genetic relationship between potential mates and helps breeders understand how genes may be concentrated within future generations. Used wisely, COI supports thoughtful preservation breeding by encouraging breeders to consider both genetic diversity and predictability.

However, COI is not a scorecard for breeding quality, nor should it become the sole basis for breeding decisions. Outstanding preservation breeders recognize that health, temperament, structure, longevity, fertility, pedigree strength, and breed type cannot be reduced to a single percentage. Instead, they integrate COI with comprehensive health testing, careful pedigree evaluation, family history, and years of practical observation.

Ultimately, successful breeding is not about achieving the lowest COI possible—it is about making informed decisions that preserve the health, function, character, and genetic future of the Bedlington Terrier. Great breeders understand that COI measures relatedness; wisdom determines how that information is used.