Spitz inbreeding: how to assess a proposed pairing

What COI describes

The coefficient of inbreeding estimates the probability that two copies of a genetic variant descend from a common ancestor. It describes relatedness, not the chance that a puppy will be ill. A result of 6% does not mean six affected puppies in every hundred.

[1] Nordic Kennel Union Scientific Committee — Pedigree and genomic inbreeding

Why calculators can disagree

A short pedigree and a many-generation pedigree provide different amounts of information. Ask about method, generations and missing entries. A zero based on unknown ancestors is not evidence that the parents are unrelated.

[1] Nordic Kennel Union Scientific Committee — Pedigree and genomic inbreeding

Pedigree and genomic estimates

Pedigree COI is calculated from recorded relationships between ancestors. Genomic methods examine DNA directly and may detect accumulated relatedness missing from a short pedigree. Results produced by different methods should not be placed on the same scale without an explanation from the laboratory.

A panel for individual diseases is not a genetic-diversity assessment. Two Pomeranians testing negative for several known mutations can still be close relatives. Before ordering a test, decide whether the question concerns parentage, a particular disease or genetic diversity.

[4] Bannasch et al., 2021 — Inbreeding, body size and health in dog breeds

Examples of close relationships

In a simplified pedigree with no earlier inbreeding, a parent–offspring pairing or a pairing of full siblings gives an expected offspring COI of 25%. Half siblings sharing one parent give 12.5%, and first cousins give 6.25%. Relatedness accumulated in previous generations changes the result.

These examples explain the scale; they do not establish an acceptable mating threshold. Comparing a pairing with a breed average is useful only when the underlying data are comparable. An average describes a population rather than defining a medically safe boundary.

[4] Bannasch et al., 2021 — Inbreeding, body size and health in dog breeds

What related breeding changes

Related mating increases the chance of matching inherited variants, including unwanted ones. A previous healthy litter cannot establish that repeating the pairing will be safe for every future puppy.

[2] FCI — Memo on inbreeding

Compare candidates on equal terms

Make a working table with identity, common ancestors, COI calculation, examination results, diagnosed family conditions and available information about offspring. Leave unknown fields blank. An owner who reports no problems has not supplied a normal test result.

Use the same pedigree depth for each candidate. If one family is well documented and another has many gaps, the lower number may reflect missing information. Request the underlying pedigree, rather than only a calculator screenshot.

Why excessive use of one sire matters

Show success can lead to one male producing many offspring, followed by extensive breeding from his sons and daughters. After several generations, unrelated partners become harder to find within that part of the population. This can happen without anyone deliberately mating close relatives.

Consider future options for the offspring as well as the immediate litter. A less famous, healthy male from another well documented family may be more useful than repeating the most popular combination. This does not justify skipping examinations or assuming that an imported dog is unrelated.

[5] FCI — International Breeding Strategies

Questions to resolve before breeding

Ask why this particular relative was chosen, which alternatives were considered and how offspring health will be followed. An answer consisting only of an ancestor’s show titles provides little information about risk.

Save the calculation, date and original pedigree. After a litter is born, record actual observations and confirmed diagnoses. An organised record is more useful than a claim that a family has never had illness. No reported disease and normal findings from an appropriate examination are different kinds of evidence.