Many races created by humans come from consanguineous marriages whose purpose was to fix certain physical or behavioral characteristics. But with the elements of beauty, genetic diseases have sometimes come to invite themselves that inbreeding has allowed to spread in families of cats. This is why today, in order to enlarge the gene pool of a breed, some breeders practice outcrossing, or external crossing which consists of an integration of “new blood” into the bloodlines.
Explanations on outcross cats their usefulness and disadvantages.
What Is Inbreeding In Purebred Cats?
In some breeds of cats, very few specimens have been used during the foundation of the first lines. In the Maine Coon, for example, only 5 individuals, called the Top 5 (top five) were used to set the characteristics of the breed. These cats still represent 70% of the genetic heritage of so-called traditional Maine Coons today. They are therefore found almost everywhere. Thus, when you mate 2 cats, they carry the same ancestors in their family tree, even if these 2 cats come from very distant cities or countries.
From the beginning, the descendants were mated between members of the same family in order to maintain the desired physical appearance as well as certain character traits.
Mother-son, father-daughter, brother-sister… Breeders have broken the taboos concerning cats. Also in the Maine Coon, the first descendants were so similar that they were called “clones”. They make up the remaining 30% of the breed’s genetic heritage.
Alongside the attractive physical specificities conforming to the standard, so-called genetic diseases have appeared which have also become fixed. Indeed, when two individuals carrying the same disease are married, it has a greater chance of being transmitted than during a marriage between a carrier individual and a healthy one. Just as the presence of the same gene gave a beautiful size, a beautiful muzzle, a superb coat, the pooling of mutated genes caused their transmission and their fixation. Furthermore, the gene pool restriction causes a immune weakness which makes cats vulnerable to viruses, bacteria and even contributes to the development of certain cancers.
The most well-known genetic disease is HCM or CMH, a heart disease that is frequently found in Maine Coons. This brought many losses and then, when possible, the implementation of screening tests. Similarly, in the Persian and the Sacred Birman, PKD, a famous hereditary kidney disease, is a consequence of consanguinity.
Some breeders, tired of seeing pretty sick cats, have started implementing new programs in their cattery to eradicate disease without compromising the appearance of the animals. They therefore incorporated outcross cats that is to say bringing new blood, blood from outside.
Inbreeding Test In Cats: How To Know?
You can check the inbreeding coefficient of his purebred cat on the Pawpeds site which lists, since the year 2000, most cats with a pedigree, as well as dogs, horses, ferrets… Today, several tens of thousands of animals are registered there. The site also allows you to carry out a test marriage in order to calculate the rate of consanguinity which would affect the possible kittens.
The Pawpeds Database however, has a limit. Only voluntary breeders register their cats there. This means that a professional indulging in unbridled inbreeding will have little desire to register his cats in the registry. When we know the parents or grandparents and provided that they were born at another breeder and registered by the latter, we can enter their name in the Pawpeds family tree to calculate the rate of cats that come from them, but it becomes more complicated and it is not always possible.
The other limit comes from the fact that a breeder can quite well register a breeder as the parent of the cat in question when the real parent is another of his breeders. The only way to be sure of the bloodlines is to require the breeder to carry out parentage testing tests recorded in the pedigrees, but not mandatory.
Acceptable Inbreeding Rate In Cats
According to genetic researchers, the inbreeding coefficient should not increase by more than 0.25% to 0.50% per generation, if we go back to all marriages. Beyond that, health problems related to inbreeding emerge. Sometimes, weaknesses and illnesses take several generations to appear, but once they appear, they are difficult to eradicate in a breed, which can be seen in the Maine Coon with HCM.
On a single marriage observed, only first cousins are acceptable (6.25%), and not rates of 25% which correspond to marriages between brother and sister or between a father or a mother and his direct descendant, which can immediately cause problems on a staff.
THE number of generations over which the inbreeding rate is calculated is very important. Indeed, the more generations we know, the more this rate rises since it is added to each of them. However, when we want to stop seeing this rate increase with each generation, the introduction of a outcross cat is one of the solutions.
Outcrossing, To Limit Inbreeding And Its Disadvantages
Breeders in the state of Maine in the USA, where the Maine Coon breed originated, created new bloodlines using alley cats that resembled Maine Coons, which they incorporated into their breeding programs. So they married Maine Coons with street cats with similar physical characteristics. The latter were recorded in the pedigrees under the name ” foundation cats or “F1”. Their kittens are therefore F2. We go down to F5 and then we consider that the descendants are classic Maine Coons. F2 cats are said to be outcross when:
- Their inbreeding coefficient is less than 10%
- The Top 5 appearing in their lines constitute less than 50%
- Clones are less than 20%.
Thus, the inbreeding coefficient ceases to rise with each generation and the gene pool is enlarged in order to limit immune weakness and certain genetic diseases associated with the breed.
Did you know ?
In France, cats registered between F1 and F5 benefit from a RIEX pedigree that is to say that they go down, between the 1e and the 4e generation, of a marriage not authorized by the LOOF. It is a pedigree which is presented like the others, but the mention “Riex” is added.
This principle of outcrossing is not the prerogative of Maine Coons. It is also used in Sphynxes, for example, which also suffer from HCM, as well as in the breeding of rats, dogs and other livestock species. This technique does not make it possible to eradicate diseases, but to limit their transmission. Sometimes recessive genes (those that are not visible and do not develop the disease) are passed on anyway. They can, during a cross, meet a similar gene, also recessive, and lead to the development of the pathology. Additionally, the outside animal may also come with new illnesses that were not associated with the breed. He then makes them enter the genetic heritage of the descendants.
Inbreeding between healthy animals and animals not carrying mutated genes (dominant or recessive) can quite well give rise to a healthy line, whereas poorly controlled outcrossing can bring in new pathologies. It is therefore balancing act and selection which requires a long perspective on the lines, screening tests when they exist and very careful monitoring of the animals resulting from the crosses.
Breeding work is therefore far from the idea that we can have of it if we imagine that it is enough to cross a male and a female to obtain a litter.