Breeding by numbers - what do the percentages mean?

Maine Coon breeders often give a few percentages of their cats pedigrees, here I give a little insight into what is behind these numbers.


I would like to start with the term foundation. Foundation cats are the first cats from which a breed emerged. Since the Maine Coon is a naturally created breed, these are long-haired "domestic cats" from North America, especially from Maine and the surrounding states. The first foundation cats date from the 1960s.

For Maine Coon, it is still allowed to include new foundation cats in the breed. However, great attention must be paid to the origin of these cats. Before thinking about using a cat as a new foundation for breeding, it is necessary to research its origin to ensure that it is by no means a crossbreed from existing breeds, or even a Maine Coon from the existing gene pool without a pedigree. Only cats that are purely natural "domestic cats" should be used as a foundation, so they should preferably come from isolated farms in Maine, where interference from pedigree cats can be excluded.

Top 5

The Top5 are 5 foundation cats born in the 60s, which are represented disproportionately often in all pedigrees. In order of frequency, these are:

The average pedigree of the 1990s is believed to be 65-70% of the top 5 cats. In the meantime (2020) these numbers have risen sharply for the widespread lines, values of 72-75% are common there today. For me personally this is too high, I try to stay below 70% as much as possible, ideally even below 60%.

As a natural breed, the Maine Coon could and should have been based on hundreds of different foundation cats. In fact the Maine Coon is based on hundres of foundation cats, but not evenly distributed. If more different foundation cats were represented in equal proportions in the pedigrees, this would make up a share for 5 cats of less than 10% instead of 70%. It is a fact that the breed can now be traced back to 2/3 (now already 3/4) to only 5 cats, which is irreversible. However, breeders should try not to let the proportion of the Top 5 increase even more, but instead to get a little bit lower by using lines with lower Top 5 percentage or new foundation lines.

In the pedigree database Pawpeds you can see all the pedigrees entered there, or put together test matings yourself, if only the parents (or grandparents) are entered. The percentage of the Top 5 can be found under the link "Foundation" which is displayed above the pedigree. There is also a list of all Foundation cats in the cats pedigree.


The high percentage of Andy, Bridget, and Dauphin probably depends on the popularity and widespread use of the "clones".

In 1978 Heidi Ho Sonkey Bill was born, a grandson and great-great-grandson of Andy and Bridget Katt of Heidi Ho. In connection with Tanstaafl Polly Adeline it was surprisingly shown that all of their descendants looked the same, just like clones…. So when we speak of the "clones" today, we are talking about the children of Sonkey and Polly. The special thing about the clones is that they were used very often in breeding because they produced cats that had a nice show quality and size. So some breeders decided that if little is good, more is better ... and there was a lot of line breeding with them and their offspring.

From time to time there are other cats that appear to often in pedigrees and thus reduce the genetic diversity. A few decades ago this was e.g. Hillside Mr. Spock. In shaded breeding, it is Belushies Utha that can be found in most pedigrees in ten generations in double digits. Such frequently represented cats should be avoided so that they do not become the next clones. Every breeder should therefore keep an eye on his pedigrees to determine whether certain cats appear too often in the lines, and not to accumulate these more in further matings.

Today most Maine Coon cats have pedigrees with 35% clones, sometimes up to 50%. Since the pedigree of the clones consists of 91% of the Top 5 cats, these two values are closely related. With a high proportion of clones, the proportion of the top 5 is automatically high, with a low proportion of clones this is usually also the case for the Top 5.

The percentage of clones can be found in Pawpeds above the pedigree under the link "Clones".


COI means coefficient of inbreeding. Maine Coon breeders usually speak of the complete inbreeding across all generations up to the beginning of the breed in the 1960s. This should not be confused with the inbreeding value over 4 generations, which is normally 0%. For the complete inbreeding value you have to click on the underlined word "Inbreeding" in Pawpeds above the pedigree, after that it says "Complete inbreeding" and the percentage. It is also important for the assessment of the COI that the "Reliability of analysis" behind the link Foundation or Clones is at least 98%. This number shows how completely the pedigree is entered in Pawpeds, since of course only a completely entered pedigree can also be fully calculated.

What does this complete COI mean? The ideal COI is below 10%, which is difficult to achieve with the existing gene pool with the high proportion of Top 5. A COI above 10% is therefore also acceptable, but should not be too far above it if possible. Many lines now have a COI of 15-20%, which is not desirable. A COI over 20% should definitely be avoided, since it only arises from very close pairings.

As with the other percentages, the lower the better. Although a one-time high COI does not mean something bad, permanent breeding with high inbreeding values can have an overall negative effect on the vitality and the immune system of the cats. Breeders should therefore keep an eye on all the values of their cats, and not always mate closely, but at least reduce the inbreeding values after a close mating in the next generation.

© This text is from Britta Singethan. It can be published on other sites, if a reference to the author and a link to the homepage is attached.