My belief is that the whole purpose of cat breeding is to selectively breed cats which have as near as possible a perfect appearance according to the breed standard and in order to achieve this the breeder has to ensure that the genes of a first-class cat are transferred to their offspring and so on down the line. The cats become progressively more homozygous. They become progressively more inbred. The problem with the process is that if there is a recessive gene which is defective it can become visible in the anatomy of the cat resulting in a condition which is undesirable.
It seems to me that cat breeding is by definition inbreeding and you can’t get around that basic premise. It depends how far you go in the process of inbreeding. It can be of various strengths and “in some limited circumstances it might be desirable to inbreed closely and, in others, significantly less closely”. The quote comes from Robinson’s Genetics for Cat Breeders and Veterinarians“.
Over time, a certain amount of inbreeding may occur within the kittens from the particular cattery, so that it may be legitimate to speak of a bloodline, – Robinson’s Genetics for Cat Breeders and Veterinarians
Cat breeders are involved in line breeding as I understand it. And the word “line” in this instance means a line of parents and offspring all of which have the same foundation cat and the same genes as near as possible. Most genes produce a cat which is very much in line with the demands of the breed standard. That, as mentioned, is my understanding of the process.
In cat breeding language, inbreeding produces (1) a steady decline of heterozygosis and (2) a steady fixation of all genes and (3) increasing genotypic similarity.
Intense inbreeding occurs when say a brother is bred to a sister or a parent to their offspring. Inbreeding can bring about a decline in health of the cat which is called inbreeding depression. I have a page on that and if you want to read it you can click on this link. When inbreeding depression occurs the only option is to outcross “only unrelated stoock”. In other words the breeders introduces fresh genes into her line to make the cats more heterozgous.
It seems to me that cat breeders have to walk along this narrow line seeking the right balance between inbreeding to fix the desirable traits of their cats against the downside of inbreeding mentioned above.
Inbreeding can bring to light genetic defects which may be latent in the cats. Random breeding tends to keep defects hidden or prevents their re-occurrence except occasionally. A recessive anomaly can be brought into the breeding programme through inbreeding.
It is notable that Robinson’s Genetics for Cat Breeders and Veterinarians has quite a large section on inbreeding and how to balance it against health and how to avoid the downsides. This in itself confirms that the concept of inbreeding is inherent in the creation of purebred cats. The classic example of inbreeding does not concern domestic cats but wild cats, specifically the white tiger. All of them that you see in zoos come from a single male whose mother was shot dead by a hunter (there are no longer any in the wild). White tigers are heavily inbred and many are born with horrible defects kept hidden from public view.
I would welcome the import of a cat breeder or any other expert on this matter.
P.S. the average lifespan of purebred cats is shorter than that of random bred cats which highlights how inbreeding negatively impacts health. For breeders the prime objective is appearance – is it a match to the breed standard? – and behaviour comes second. Health is third.