What is inbreeding?
Inbreeding occurs when relatives or closely related individuals are mated together. For example, half brother and half sister, father and daughter, niece and nephew or grandmother and grandson. We speak of inbreeding when there are double ancestors within the last 4 generations.
Sometimes breeders deliberately use inbreeding. Inbreeding is in fact the simplest way to pass on certain characteristics of the parent animals to the offspring and thus "record". At the same time, it can also magnify the bad traits or give hidden harmful recessive genes a chance to manifest. As a result, genetic diseases and defects can suddenly come to light. With inbred matings you take a big risk.
Each gene consists of two alleles, one from the father and one from the mother. By applying inbreeding, homozygosity is increased: this means that there is a greater chance that the offspring will receive two exact same alleles from the parents per gene. As a result, inbreeding leads to a narrowing of the gene pool (lower genetic diversity).
What is line breeding?
Line breeding involves mating with cats that are related, but not in the first degree. In line breeding, the relationship is much further away than in inbreeding. Line breeding combinations, for example, share the same ancestors from 4 or 5 generations ago. In this case, the breeder does not use direct inbreeding, but still gets offspring with a higher inbreeding percentage than the parents. Line breeding is a weakened form of inbreeding, which is widely used in the breeding world. Line breeding also leads to a lower genetic diversity, but with a smaller step than with an inbred mating.
The inbreeding coefficient (hereinafter referred to as inbreeding %) calculates the probability that 2 alleles can be the same (homozygous) by calculating the relationship in the ancestors.
Examples of an inbreeding coefficient are:
Mating between brother and sister: increases the inbreeding % of the progeny by 25%
Mating between parent and child: 25% increase
Mating between half brother and half sister: increase of 12.5%
Mating between grandparent and grandchild: increase of 12.5%
Cousin mating: 6.25% increase
The inbreeding % is a probability calculation of the homozyosity of the genes. If you want to actually measure this, you can do this via a DNA test. Thousands of genes are examined in the DNA to see whether these 2 have the same or 2 different alleles. MycatDNA is a lab where you can have your cat's genetic diversity tested.
Inbreeding and health
An inbred or line breeding mating can have direct consequences for the health of the offspring. But sometimes it can take several generations before the problems become apparent.
Many studies have been done on the effect of inbreeding on a population. This shows that the main risks and problems that can arise from inbreeding depression are the following:
weaker immune system and therefore increased risk of diseases and disorders (for example, FIP, cancer at a young age, infections, allergies and dental problems)
fertility problems (low sperm quality or inability to conceive)
reduced reproduction (small litters)
smaller survivability kittens
lower birth weight and/or the kittens grow less well
increased risk of stillborn kittens
facial asymmetry, mismatched jaws
Genetic variation is therefore important to keep the breed healthy. In principle, a cat with more genetic variation has a stronger immune system and more possibilities to make antibodies that can be used to overcome diseases.
What is a responsible inbreeding percentage?
The average inbreeding % of the Maine Coon breed in 2018 is 14.3% and has an increasing trend. This means that the average Maine Coon's parents are more closely related than a half-brother and half-sister. This trend could eventually lead to more visible signs of inbreeding depression. A breeder who works with higher inbreeding percentages or who deliberately uses line breeding must be well aware of the risks within the family line. Even though there are no known health problems in the ancestral lines, you still take the risk that recessive genes show up with a problem.
Although it is difficult to set a hard limit, I would personally recommend that as breeders we should aim for a total inbreeding percentage lower than 10%. When your breeding stock has a higher inbreeding percentage, you as a breeder can lower the inbreeding percentage of the offspring by looking for an unrelated partner. This allows you to lower the inbreeding coefficient a little further with each generation.
Some nuance is in order. Because a Maine Coon with a healthy inbreeding percentage can still get sick or get a hereditary disease. After all, the inbreeding percentage says something about the diversity of the genes, but not about the "quality" of the genes. Conversely, a Maine Coon with an inbreeding percentage of 25% can be very healthy and have healthy offspring. The chance of it happening is statistically much smaller. The inbreeding percentage does not say everything, but it is an important indicator that can be taken into account in the overall picture of a cat. Many other factors also come into play here. Fully tested and healthy ancestors are a telling and at least as important indicator of healthy offspring.
How can I find out the inbreeding percentage of my cat?
Do you want to buy a kitten and know the inbreeding percentage? In Pawpeds you can easily find out the total Inbreeding Percentage of your cat. When you look up your cat's pedigree name in the Pawpeds Maine Coon database , you will see the total inbreeding percentage when you click the "Inbreeding" link ("Inbreeding" when using the English settings). The link then changes to the text "Total inbreeding" and shows the total inbreeding percentage after that, taking into account all known ancestors registered in Pawpeds.
The video below shows you how to do this.
If you do not want to see the total inbreeding % but the inbreeding up to 6 generations back, click on the number 6 next to Generations. You can do the same for generations 2 to 10, by clicking on the corresponding number.
Assuming all information in Pawpeds is correct, Pawpeds also provides a confidence factor for the calculated inbreeding percentages. You can see this when you click on the "Foundation" link in the screen that shows the family tree. For example, it says this: " Reliability of analysis 99.0% (1.0% undetected to foundation)". Below is a list of well-known Foundation cats that are the primeval fathers and mothers of your cat. Further down the page under the heading "Cats not traced to foundation" are your cat's unknown ancestors (the 1% unknown) that were not submitted to Pawpeds. In this example, the total inbreeding % can be up to 1% higher if the indicated missing cats are entered in Pawpeds. When the percentage unknown is higher than 2%, Pawpeds will give a warning and the text will be colored red.
Pawpeds gives the following advice to breeders:
When you look at every single mating of the past 5 generations, the average inbreeding % of all these matings together should not exceed 2.5%. If you do the same for the previous 10 generations, the average should not exceed 5%. Most Maine Coons with a high percentage of inbreeding meet this requirement. In this case, the kinship is with the ancestors going back more than 10 generations. See also the article on the clones .
When planning a mating, you should not mate relatives closer to each other than cousins (this increases the inbreeding rate of the offspring by 6.25%). This is to prevent direct health problems for the offspring.
With each mating you do, inbreeding % should not increase more than 0.25-0.5% to avoid an increased risk in the next generation.
My cat is not in Pawpeds
If your cat is not registered in Pawpeds, you (both enthusiasts and breeders) can easily do this by sending a copy of the pedigree by email to Leonie van der Belt. She ensures that the family tree is registered in the public Pawpeds database . If the parents or all grandparents are in Pawpeds, you can still find out the inbreeding percentage by making a test mating in Pawpeds.
To keep the breed healthy, the inbreeding coefficient is an important indicator to prevent the aforementioned health problems. A breeder cannot do this alone, cooperation is necessary. More breeders are needed who see the need for this and who want to make an active contribution to the health of the breed.
A frequently heard argument for not doing this is because the progeny may be less typified. Although you get more variety in the appearance of your kittens with unrelated cats, they don't necessarily have to lose type. Unless you choose a mating with a male (or female) that has too little type or select a kitten for breeding that is less well typed than a littermate.
If you have any questions about this article, do not hesitate to contact me via the chat function or the contact form .
User guide (Pawpeds)
Family tree (Mainecoon.nl)
Li, X, “Inbreeding depression in captive animal populations”, (2014) Faculty of Science Theses