Judging a mating means separating what the pairing produced from what either parent would have produced with anyone else — a distinction a single litter is almost never large enough to settle.
The most important first
- A combination, a dam and a sire are three different things under evaluation, and one litter cannot tell them apart; treat the combination as a hypothesis you have tested once.
- Inbreeding coefficients describe the pairing, not the puppies: the Royal Kennel Club calls a coefficient a measure of risk rather than a direct measure of health, with roughly 12.5 percent corresponding to a half-sibling mating and 25 percent to a full-sibling or parent–offspring mating.
- Pedigree analyses suggest holding the increase in kinship to no more than half a percentage point to one percentage point per generation, which is a property of your planning, not of any one litter’s outcome.
- A repeat mating or a sister combination is the only test of a combination available to an individual breeder, and it is a weak one; plan it as a test and say in advance what would change your mind.
- Read this after evaluating the whole litter and alongside dog breeding systems.
Three things, not one
When a litter turns out well, three explanations are available and they are not the same. The dam may be a good producer with almost any partner. The sire may be. Or the particular pairing may have combined in a way neither does with other mates, because the alleles they contributed complemented each other. Breeders routinely collapse all three into a single judgment about the mating, and that is where the trouble starts.
Pulling them apart requires information from outside the litter. If the dam has produced well with two unrelated sires, her contribution is the simplest explanation and the combination adds little. If the sire has forty offspring from many dams and they are consistently sound, the same applies to him. A true combination effect — a result neither parent gives elsewhere — can only be inferred when both parents have a track record with other partners, and most breeders are evaluating a sire with few offspring and a dam with two or three litters.
So the honest first step is to write down what you actually have: how many litters the dam has had and with how many sires, how many offspring the sire has and how widely spread, and how much of the breed’s own data is available on both. The structure described in pedigree analysis tells you how the two dogs are related; it does not tell you what they produce together, and the two questions are often confused.
Chance in a single litter
Each puppy receives one of an enormous number of possible combinations of its parents’ alleles. A litter of six samples six of those. Mate the same pair again and you sample six more, and they will differ. This is not a caveat to be mentioned and then ignored; it is the dominant source of variation in what you are looking at.
The practical implication is that the spread of outcomes in a litter is largely uninformative about the pairing, while the extremes are the least informative part of all. One outstanding puppy among six does not establish that the combination produces outstanding dogs, and one affected puppy does not establish that it produces disease, although for a recessive condition it does establish that both parents carry the variant, which is a different and much firmer kind of information.
The asymmetry is worth holding onto. A single litter can prove a carrier status, confirm that a structural fault is transmitted, or demonstrate that a mating is reproductively viable. It cannot demonstrate that a combination is better than the alternatives. Positive conclusions need much more material than negative ones, and the reasoning in population genetics for breeders explains why.
Did the breeding system do what it was for
A combination is usually chosen under some system: a linebreeding intended to consolidate a type, an outcross intended to bring in something missing, or a planned pairing of complementary faults. That intention is testable in a way the general question of quality is not, and it is the part of the evaluation where a single litter actually carries weight.
Ask what the system predicted. A linebreeding should have produced greater uniformity than an outcross would, whether or not the type is the one you wanted. An outcross should have produced more variation, and possibly less of the breed character you had been maintaining. A complementary pairing should have produced puppies intermediate between the parents in the specific trait you were addressing, not a mixture of puppies resembling one parent or the other. If the litter did not behave as the system predicts, the useful conclusion often concerns your assumptions about the two dogs rather than their quality.
Where the intention was to improve one defined trait, judge it on that trait and resist the urge to re-score the whole litter. A mating that fixed the shortcoming it was designed to address, and cost you something elsewhere, has given you clear information. The reasoning behind each approach is set out in dog breeding systems, and the evaluation is only as good as the written intention it is measured against.
Some effects of a closer pairing show up in the litter itself. In a study of seven French breeds, inbreeding in both the dam and the litter was linked to smaller litters, and matings between close relatives were linked to shorter lives. Litter size, puppy survival and how long the dogs live are worth recording as part of judging whether the combination worked. The Royal Kennel Club generally will not register puppies from full-sibling or parent–offspring matings, and the FCI advises never to make them, so those combinations are off the table regardless of the figures.
What the kennel clubs say
Some national clubs ban these matings outright. The Swedish Kennel Club (SKK), for example, does not allow father–daughter, mother–son or full-sibling matings.
Source: Swedish Kennel Club (SKK), Basic rules (Grundregler), in force from January 1, 2026.
Last updated: November 8, 2026
Rules change, so always check with your own kennel club.
Inbreeding figures describe the pairing, not the puppies
The coefficient of inbreeding for a combination is calculated before the mating and does not change afterward. It is a property of the pairing, and the Royal Kennel Club is careful to describe it as a measure of risk rather than a direct measure of health: a higher figure raises the probability of two copies of the same ancestral variant meeting, but it does not say whether that happened in these puppies. Its published reference points put roughly 12.5 percent at the level of a half-sibling or grandparent mating and 25 percent at a full-sibling or parent–offspring mating, with breed averages recalculated annually so that a planned mating can be compared against the current population rather than against history.
How much weight the figure can carry depends on the pedigree behind it. Calculations use all electronically held generations, so a dog with nine recorded generations and an import with three are not comparable at all, and the lower figure on the import is an artifact rather than a reassurance. Published analyses of four well-recorded French breeds report pedigree completeness of roughly seven to nine equivalent generations, and mean coefficients in the range of about 0.056 to 0.091 across the breeds studied.
At breed level, higher inbreeding is associated with more veterinary morbidity: an analysis across 227 breeds found a mean adjusted coefficient of 0.249 (measured from DNA, which captures inbreeding far back beyond any written pedigree, so it is not comparable to a pedigree COI) and morbidity rising from around 1,282 to 1,626 care events per 10,000 dog years at risk between the least and most inbred groups. That is a population-level association using breed averages, and several breeds did not follow it. In the same study, body size was an even stronger predictor of morbidity than inbreeding. It is a reason to manage inbreeding in your planning, as described in the coefficient of inbreeding, and not a diagnosis of any litter you have bred.
Two kinds of inbreeding figure are in use, and they are not interchangeable. A pedigree COI, such as the one from a kennel club calculator, counts only the generations on record. A genomic figure from a DNA test picks up shared ancestry far further back. That is why a DNA-based breed average of around 25 percent and a pedigree COI of 6 percent for your litter can both be true. Compare like with like: a pedigree COI against the breed’s pedigree average, and a genomic figure against genomic breed data. At breed level, the rate at which inbreeding rises each generation matters more than any one litter’s figure; a widely used ceiling is about one percentage point per generation. No single COI level is known to be the point at which health suffers; much of the risk depends on which harmful recessive variants the breed’s founders happened to carry.
Repeating, varying or abandoning
Having evaluated the combination, you have three options, and each is a different experiment. A repeat mating tests the combination again with a second sample, which is the only replication available to a breeder; it is weak, but it is real, and it is the only way one kennel can distinguish a promising pairing from a lucky one. A sister combination — the same sire to a close relative of the dam, or the reverse — tests whether the effect follows the line rather than the individual. Abandoning the pairing closes the question without answering it.
Treat a repeat as a test rather than a reward. Decide beforehand what would count as confirmation and what would count as disconfirmation, and write it down, because after the puppies arrive the criteria have a habit of adjusting themselves. Decide beforehand, too, what the repeat costs the breed: a pairing repeated several times concentrates the same ancestors, and the Fédération Cynologique Internationale discourages heavy repeated use of individual dogs, recommending that no dog produce more than about 5 percent of a breed’s puppies over five years.
That percentage translates very differently between breeds. In published analyses the same rule worked out at fourteen offspring in one numerically small breed and well over a thousand in a popular one. Simulations in those breeds suggest that capping how much each sire contributes measurably slows the rise in kinship: in one French breed, the Coton de Tulear, a cap of fifty offspring per sire would have lowered mean kinship by about 15 percent, while in the smallest breed studied a very low cap of 25 actually raised it, so the right cap differs by breed. Those are decisions about program structure, taken in long-term breeding program terms, and they are decisions you can get right without having resolved anything about the combination at all.
In practice
A breeder’s second litter from a linebred pairing of a dam and a sire sharing a grandsire produces five puppies that are strikingly uniform in type, with two showing the shoulder placement she had been trying to fix and none showing the loose hocks that had worried her in the dam’s line. Her instinct is that she has found the combination. Writing it out instead, she notes that the dam has only ever been bred to this sire, that the sire has nine offspring in total, and that she therefore cannot separate a combination effect from the sire simply being good. The uniformity is what the linebreeding predicted and is not in itself evidence of quality. She plans one repeat, writes down in advance that she will consider the pairing confirmed only if the shoulder improvement appears in at least half of the second litter, and separately books the dam’s half-sister to an unrelated sire so that the sire has offspring from a second dam line to be judged on.
(Illustrative, composite scenario.)
Work on it
A few minutes here will teach you more than re-reading the article.
Ask yourself
- For the combination I am evaluating, how many litters has the dam had with other sires, and how many offspring does the sire have from other dams?
- What did the breeding system I chose predict, and did the litter behave that way regardless of whether I liked the result?
- If I repeated this mating, what outcome would make me abandon it?
Find out & check
- Find out how many recorded generations lie behind the inbreeding coefficient you were given for this pairing, and what the current breed average is.
Do one thing
- Write a single paragraph stating what this combination gave that neither parent has given with other partners, and mark honestly whether you have enough information to say.
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Sources & further reading
- Fédération Cynologique Internationale — FCI international breeding strategies. fci.be
- Leroy G. & Rognon X. — Assessing the impact of breeding strategies on inherited disorders and genetic diversity in dogs. vin.com
- The Royal Kennel Club — Inbreeding coefficients and inbreeding calculators. royalkennelclub.com
- Bannasch D., Famula T., Donner J., Anderson H., Honkanen L., Batcher K., Safra N., Thomasy S. & Rebhun R. — The effect of inbreeding, body size and morphology on health in dog breeds. escholarship.org
- Lewis T. W., Abhayaratne B. M. & Blott S. C. — Trends in genetic diversity for all Kennel Club registered pedigree dog breeds. cgejournal.biomedcentral.com
- Leroy G., Phocas F., Hedan B., Verrier E. & Rognon X. (2015), The Veterinary Journal — Inbreeding impact on litter size and survival in selected canine breeds. sciencedirect.com
- Jerold S. Bell, DVM (Tufts, via VIN) — Small Population Breeds and Issues of Genetic Diversity. vin.com
Where evidence is limited, recommendations rest on established practice and expert judgment, and may be updated as knowledge develops. A judgment about a combination rests on one or two litters, which is far below any threshold for statistical inference, so what is being evaluated is the quality of the reasoning and the decisions that follow, not the significance of a difference.
Next steps
- Read next: Evaluating the dam and sire over time.
- Related: Pedigree analysis · Making the next generation’s breeding decisions.
- Return to the area hub: Closing the loop: follow-up and the next generation.