Master Dog Breeders and Associates –
Easy Guide to Building Lines in a Developing Breed
These apply to not only managing diseases, but also to building your own lines for or against specific traits. Every litter should move you closer to your goals – whether that’s stronger health, stable temperament, or refining a type.
Key Genetic Tools: COI and Heterozygosity
Before planning a litter, you need to understand two simple measures that tell you how wide or narrow your genetic base is.
Coefficient of Inbreeding (COI)
- What it means: COI measures how closely related the parents are. It’s like a “family tree overlap score.”
- Why it matters: The higher the COI, the more chance hidden health problems can surface.
Heterozygosity (Genetic Diversity)
- What it means: This measures how much variation sits within a dog’s DNA.
- Why it matters: Higher scores usually mean more resilience and adaptability, while lower scores suggest the gene pool is tightening.
The Traffic Light Guide
Green (Low COI, Higher Heterozygosity): Plenty of breathing room in the genes. Good for widening the pool and protecting health.
Amber (Moderate COI, Moderate Heterozygosity): Common in purebreds. Safe if balanced with good health testing and careful mate choice.
Red (High COI, Low Heterozygosity): Use with extreme caution. Only deliberate, short-term, and with a plan to bring balance back in the next generation.
Acquire the Gene or Trait Once – Don’t Collect It Everywhere
Think of a muddy boot in your clean house. One is easy to clean. Ten make a mess.
- Health: If you bring in one carrier of a problem gene, that’s enough. Track it and manage it carefully.
- Traits: If you bring in one dog with the coat, size, or temperament trait you want, that’s enough too. Don’t “collect” it from multiple sources or you risk narrowing your lines too fast.
Whether it’s a gene or a trait, acquire it once and manage it deliberately.
Breed It Forward for Three Generations
Think of this like climbing a ladder.
- Step 1: Pair your foundation dog with something that balances it – clear health, sound type, good temperament, and preferably a lower COI or higher heterozygosity partner.
- Step 2: Choose the best puppy to carry forward the trait (or to carry the health gene responsibly).
- Step 3: Repeat twice more. After three generations, you’ve stabilised that trait in your line while also keeping diversity intact.
This is how you build lines – by carrying traits forward deliberately, not by chasing them all over the breed.
Know What You Have – Know What You Need
- Health: DNA, health testing, vet checks.
- Temperament: Calm, biddable, confident?
- Structure: Is movement, coat, size, or bite correct?
- Genetics: What’s your COI and heterozygosity score?
Don’t breed blind. Measure before you move forward. Otherwise, an outcross might take you backwards – reintroducing health risks or unstable traits.
Purpose of the Three-Generation Rule
- Widen the gene pool – don’t trap traits in one narrow pocket.
- Widen type choices – keep different options available for the breed’s future.
- Dilute weaknesses – balance out health, type, or temperament faults.
- Reduce popular sire syndrome – don’t let one dog dominate the breed.
- Monitor impact – see how the gene or trait develops across your line.
- Balance COI and heterozygosity – so your “traffic light” stays green or amber, not red.
Don’t Chase Unicorns
- Don’t breed two carriers just to “create” a rare outcome.
- Don’t double up traits from multiple kennels in hopes of striking gold.
- Example: If you want a calmer temperament, you don’t need to “stack” five calm lines. Acquire it once, breed it forward carefully, and balance it with other traits.
Protect the Breed – Be Careful Who You Share With
- Don’t spread carriers or traits into kennels where they already exist in high numbers.
- Don’t “collect” traits from everywhere without a plan.
Each trait or carrier should be treated as a foundation line to be carried forward with care.
Every Litter Needs a Goal
- Health Goal: Eliminate MMVD or hemivertebrae.
- Temperament Goal: Improve stability or therapy-suitability.
- Type Goal: Strengthen coat, movement, or size consistency.
- Diversity Goal: Keep COI moderate and maintain healthy heterozygosity.
If you don’t know the why behind a mating, stop and work it out before breeding.
Protecting Your Work
Every breeder invests years into building lines carefully.
- Where you place breeding dogs matters: once a line leaves your hands, you can’t control how it’s used.
- Be cautious about selling breeding dogs into programs that don’t share the same goals or standards — this can undo your work and weaken the breed.
Bottom Line: Protect your efforts and the wider breed by placing breeding stock only with those who are committed to the same responsible system.
Bottom Line
Whether you’re tackling a health gene or refining a trait, the same rules apply:
- Acquire once, don’t scatter it everywhere.
- Breed forward for three generations.
- Don’t chase unicorns.
- Set clear goals for every litter.
- Keep your genetic “traffic light” in the green or amber zones.
This is how responsible breeders build lines in a developing breed while keeping the overall population healthy, diverse, and moving forward.