Planning a Mating: How to Avoid Pairing Cats Too Closely

After more than twenty years breeding and exhibiting Siamese and Oriental cats, and judging for the GCCF since 2014, I have seen a great many mating decisions made well and a fair few made badly. The single most common mistake I come across in newer breeders is not a dramatic one. It is simply pairing two cats that are more closely related than the breeder realised, because the pedigrees looked different enough on the surface. This article is about how to evaluate a proposed pairing properly, so you can make a confident decision before the cats ever meet.

Start with the question, not the cats

Before you fall in love with a particular stud, get clear on what you are trying to achieve. Are you trying to fix a desirable trait, such as type or coat texture? Are you trying to introduce something your line lacks? Or are you simply hoping for healthy, well-typed kittens with no particular agenda? Your goal changes how much relatedness you should tolerate. A breeder consolidating an excellent line may accept a degree of line-breeding that a breeder simply producing pet and show kittens should not. There is no single correct answer, but there is a correct process.

Relatedness is not the same as a shared name

The first trap is judging relatedness by eye. Two pedigrees can look reassuringly different across the first three generations and still share a great deal of ancestry further back, particularly in numerically smaller breeds where the founding population was always limited. A single influential cat appearing twice in the fourth or fifth generation, once on the sire’s side and once on the dam’s, contributes far more shared genetic material than most people expect.

This is why I always recommend looking at relatedness across at least five generations, and ideally further where the records exist. The eye is simply not built to add up the contributions of a dozen common ancestors scattered across two five-generation pedigrees. That is arithmetic, and it is exactly the sort of arithmetic a computer should do for you.

What COI actually tells you in a mating decision

The coefficient of inbreeding, or COI, is the single number breeders reach for most often. Without rehashing the full mechanics, the useful thing to understand for a mating decision is this: the COI of the proposed litter tells you the probability that any given gene the kittens inherit will be identical from both parents because it traces back to a common ancestor. A higher figure means the parents share more ancestry, and the kittens have less genetic variety to draw on.

What COI does not do is tell you whether a mating is good or bad on its own. It is a measure of risk and diversity, not of quality. A modest figure on a wide, well-recorded pedigree is reassuring. The same figure on a shallow pedigree, where you simply do not have enough generations to see the true picture, is far less reassuring, because the real relatedness is hidden behind missing records. Treat COI as one input, read it in the context of how complete the pedigree is, and never treat a single number as a verdict.

Line-breeding versus too close

There is a meaningful difference between considered line-breeding and pairing cats too closely. Line-breeding is the deliberate, sparing repetition of an outstanding ancestor a few generations back, used by experienced breeders to fix a trait they have good reason to want consolidated. It is a tool, and like any sharp tool it should be used with respect and not on every litter.

Pairing too closely is different. Mating full siblings, parent to offspring, or repeatedly doubling up on the same recent ancestors without a clear plan stacks the odds against you. It concentrates not just the traits you want but everything else carried in that line, including the faults and the health risks you cannot see. As a rough working principle I share with the breeders I mentor: if you cannot articulate exactly which specific quality you are trying to fix and why this pairing is the way to fix it, you are probably better off opening the pedigree out rather than tightening it.

• Look beyond three generations. Shared ancestors hide in the back of the pedigree.
• Read COI alongside pedigree completeness, not in isolation.
• Only line-breed when you can name the specific trait you are consolidating.
• When in doubt, widen the gene pool rather than narrow it.

Use a trial mating to decide before you commit

The decision that used to be made on intuition can now be tested on paper first. A trial mating lets you check a proposed sire and dam before the cats ever meet, the stud fee is paid, or the queen travels. You build the hypothetical litter from both parents’ pedigrees and see what the pairing would actually produce: the projected COI, how the common ancestors stack up, and how much genetic diversity the kittens would have to work with.

In Perfect Pedigrees this is exactly how trial matings work. You select your queen and a prospective stud, and the system calculates the figures for the litter that pairing would produce, drawing on a curated pool of around 90,000 cats that has been checked by a GCCF judge. You can run the same queen against several different studs and compare them side by side, which is far more useful than agonising over a single pairing in isolation. It costs nothing to build and explore; you only pay when you decide to print a pedigree. That means you can do the homework on a dozen possible matings before you commit to one.

What I like most about doing this on screen is that it turns a vague worry into a clear comparison. Instead of saying “those two feel a bit close,” you can see that one stud gives your litter a noticeably lower COI and a healthier spread of ancestry than another, and choose accordingly. The cat fancy has always valued the breeder’s eye, and rightly so, but the eye is far better employed judging type and temperament than trying to compute relatedness across five generations in your head.

A sensible workflow for every proposed pairing

• Write down your goal for the litter before you look at any studs.
• Build a trial mating for each realistic candidate.
• Compare projected COI and diversity across candidates, not against an arbitrary target.
• Check whether any common ancestors are appearing too often, and how far back they sit.
• Factor in health testing and temperament, which no number can capture.
• Make the decision, and keep the trial mating on file as a record of why.

That last point matters more than people think. Keeping a record of the matings you considered and rejected, not just the one you chose, makes you a better breeder over time. You build up a real understanding of how your line behaves, and you can explain your reasoning to a buyer, a mentor, or a breed advisory committee with confidence.

Written by Ross Davies — GCCF Full Judge, breeder and exhibitor of 20+ years, and a qualified feline behaviourist. Perfect Pedigrees is a breeder’s record-keeping and pedigree tool, not a registering body.