The Pros and Cons of Inbreeding in Cats

Those involved with minority breeds (rare breeds) of livestock face a dilemma as they try to balance purity against the risk of genetic conformity. Enthusiasts preserve minority breeds because their genes may prove useful to farmers in the future, but at the same time the low numbers of the breed involved means that it runs the risk of becoming unhealthily inbred. When trying to bring a breed back from the point of extinction, the introduction of "new blood" through crossing with an unrelated breed is usually a last resort because it can change the very character of the breed being preserved (as noted by cat fanciers when Russian Blues were crossed to Blue Point Siamese after World War II). In livestock, successive generations of progeny must be bred back to a purebred ancestor for 6 - 8 generations before the offspring can be considered purebred themselves.

In the cat fancy, breed purity is equally desirable, but can be taken to ridiculous lengths. Some fancies will not recognize "hybrid" breeds such as the Tonkinese because it produces variants (yet Manxes are recognized and also produce variants). Breeds which cannot produce some degree of variability among their offspring risk finding themselves in the same predicament as Cheetahs and Giant Pandas. Such fancies have lost sight of the fact that they are registering "pedigree" cats, not "pure-bred" cats, especially since they may recognize breeds which require occasional outcrossing to maintain type!

The breed purity debate goes along these lines: should a breed be based on genotype (what genes it inherited) or phenotype (appearance, despite an out-cross four generations ago) A Tabby-point Siamese is phenotypically Siamese, but because the tabby patter was introduced from non-Siamese cats, genotype-followers consider it "not Siamese" and are worried it will pollute their purebred breeding lines. In some registries, Exotic Longhairs are identical to Persians, but may not be bred with Persians. Likewise, some registries do not allow chocolate or lilac Persians to be classed as Persians because the colors were introduced from Siamese cats (via the Himalayan breed) umpteen generations ago and are therefore "tainted". Those "tainted" genes may be bundled with whole lot of healthy genes; by not outcrossing "purebreds" to "tainted" cats, the opportunity to increase the heterozygosity of the immune system is lost.

One formula to reduce inbreeding and slow down the loss of vigor is to line-breed for 2-3 generation and then out-cross to an unrelated line (or occasionally another breed) to get back hybrid vigor and genetic diversity. However with the emphasis on breeding for type and competitiveness on the show bench (and when making a sale), the typey studs get used more and more often and there is less and less chance of finding a truly unrelated line.

Implications of Inbreeding for the Cat Breeder

Most cat breeders are well aware of potential pitfalls associated with inbreeding although it is tempting for a novice to continue to use one or two closely related lines in order to preserve or improve type. Breeding to an unrelated line of the same breed (where possible) or outcrossing to another breed (where permissible) can ensure vigor. Despite the risk of importing a few undesirable traits which may take a while to breed out, outcrossing can prevent a breed from stagnating by introducing fresh genes into the gene pool. It is important to outcross to a variety of different cats, considered to be genetically "sound" (do any of their previous offspring exhibit undesirable traits?) and preferably not closely related to each other. Outcrossing is made difficult by the amount of inbreeding in previous generations - it becomes hard to find cats which are not related, sometimes several times over.

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