Leslie A. Lyons, PhD
Assistant Professor, University of California-Davis, School of Veterinary Medicine, Department of Population Health & Reproduction
Davis, CA, USA
The cat has been domesticated for approximately 5,000 years. Although popular belief suggests that cats were domesticated by the Egyptians, the true origins of the domestic cat have not been clearly documented by neither archeological nor genetic data. Prior to the cat fancy in the late 1800's, several populations of cats could be clearly distinguished as breeds. Cats from Europe were stocky in build, while Far East cats had the more slender body styles and Siamese points. Most of the cat breeds, however, have been developed in the past 50 years. Of the over 50 cat breeds that are recognized worldwide, 15 breeds can be identified as the "founders" of most all current breeds. Approximately 50% of the foundation breeds are populations specific to Europe and Africa and the other half are Asian breeds. All random bred New World cats and Australian cats are primarily derivatives of European cats that migrated post-1600. The "founder" breeds were recognized both in Europe and in North America prior to WWII, which decimated many cat breeds in Europe and England. Historical records suggest that several breeds maintained stocks from their proper area of origin, such as the Korat, while some breeds had to be re-established. The foundation breeds remained true in the USA since WWII did not affect the cat fancy as it did in the war torn areas of Europe and England. Although some migration of cats between the US and Europe occurs, this is rather infrequent due to expense, efficiency, and the 6 months quarantine requirement for entrance into Great Britain due to Rabies control. Additionally, cat fancy standards are different for some, but not all breeds, between the US and Europe, thus some breeds are more likely to be interchanged that others. Due to the fact that development and gene pools of cats are specific for each breed, the breed history must be closely considered when examining cat genetics.
Genetics and Health
Some cat breeds are very popular in the United States, such as Persians, Maine Coons, Siamese and Abyssinians. Still others, such as Havana Brown, Korat, Chartreux, and Russian Blue, have much smaller followings. Larger populations have a better opportunity to diversify by migration, low founder effects and mutation, while small populations are more likely to lose genetic variation. Additionally, breeds that allow many colors suggest more breadth in their foundation than breeds that have only one or limited colors. Although color variety can be good for the population, breeders who work with only specific lines or colors could have isolated groups of cats with reduced genetic variation.
Reduced genetic variation has been to shown to predict health problems. The health issues can have a variety of presentations, some mild and some more devastating. Inherited diseases are often recognized as signs of inbreeding depression and are often single gene traits. PKD, heart disease and some cancers are caused by single genes and could be eradicated once the genes are identified. Many health problems, however, are more complex and many genes affect their presentation. Hence, eradicating these diseases is exponentially more difficult than eliminating single gene traits. In general, cats are a robust species, thus, any intervention to maintain their health should be closely scrutinized and minor things that breeders think are normal for the breed could be signs of genetic diversity loss and be complex traits. Gingivitis, dystosia, diabetes, epilepsy, reduced litter sizes, and FIP are often overlooked as to having genetics as a role in their presentation. Therefore, breeders need to consider genetic diversity while maintaining show quality cats, which can be a difficult tight rope to walk. Additionally, the push for the more extreme body conformations is inherently exacerbating conditions that could be alleviated by more moderate body styles, particularly patellar luxations in the slender and fine boned cats and dental abnormalities and upper respiratory conditions in the short muzzled cats.
Start with a Good Foundation
Maintaining genetic diversity helps stack the deck in favor of overall feline health. Thus, a good breeding program will consider maintaining genetic diversity. For the initial development of a breed, many founders should be acquired and randomly bred to diversify the initial stock that will be used for the breed development. Many breeders and large breeding groups should be established to promote a good foundation. Then, once a breeding program is "closed" to the use of various cats, good management dictates that cats get widely dispersed and particular individuals should not be over represented within a breed or line. Several breed associations often limit the use of popular sires, studs, or queens for this reason, which can be difficult because winning animals are often in high demand.
The Power of Pedigrees
Good breeding records can help predict the inbreeding coefficients of particular matings and several commercial programs can help predict the kinship of desired matings. Reducing kinship or relatedness inherently maintains good genetic diversity. Many breeders use this information to select mates and for interaction with different breeders to maintain diverse genetic stocks.
Genetics can also help to confirm good breeding records. Mistakes can easily be made with matings, thus, proving parentage can help to truly establish the breed history. Combined with microchipping, genetics can alleviate any mistaken identities or parentages within the cat world.
As important as breeding records are records for the health of the colony. Every cat should have a file that starts with time of birth and birth weight to the time and date of death. Once cats leave a particular persons care, this becomes difficult to track, but these records should always be transferred with a cat and new owners should be educated on how to maintain continuation of the records. Records should be kept of vaccinations, weights, type of food the cats receive and any health problems. Records should also include the movement of cats into and out of the cattery and housing conditions. These details help to establish the environmental exposures the cat may experience as well and introduction of new virus strains into a cattery. This information can later be used to establish whether a health condition has a stronger environmental or genetic component. Thus, if one is attempting to establish whether a breed or a line is suffering from inbreeding depression, this information helps to develop a proper evaluation.
If pedigrees cannot be maintained since the inception of the breed, genetic markers can be used to help determine the level of inbreeding depression within a breed. This level is always relative to other breeds and outbred populations, so that deciding on what level of depression is significant is difficult. Considering breed history, size and health issues will help to decide if cats are getting too inbred. Thus, the genetics is not used alone, but in conjunction with other information about the breed group.
We are collecting DNA samples from each of the foundation breeds and various worldwide random bred populations, generally via buccal swabs. The random bred populations include California, Texas and New York for the USA and Kenya, Korea, Mexico and Australia, worldwide. Breed samples are unrelated but represent strong contributors to the breed, show winners, and popular studs. For the project, approximately 60 samples will be analyzed for each breed with fifty genetic markers. We have collected and analyzed at least 25% of all but two of the populations with approximately 15 STRs. Preliminary comparisons of the populations show some cat breeds can be distinguished by unique marker alleles and different allelic frequencies. The Burmese breed shows partitioning between breed types and US versus European cats. This data will be used to develop a universal set of markers for parentage analysis and identification. We expect this data to help elucidate the migrations and development of the present domestic cat breeds and comparisons to small wildcat populations, like African, European, and Asian wildcats, may predict the true origins of the domestic cat. Cat breeders realize that genetic information can help manage their catteries and also provide breed associations with guidelines as to whether to open or close outcrossing opportunities. Genetic data could be used to help breeders select genetically diverse outcrosses and combined with pedigree and health information, could lead to healthier animals.
Genetics can help maintain healthy cat populations. If used during the development of a breed, cats could be maintained with good genetic diversity, lowering the occurrences of health problems. Many breeds, however, have been established for 50-100 years and inbreeding is already having an affect. Combined with health records, breed history and population size, genetics could help to diversify existing populations and also provide good suggestions for outcrossing programs on a periodic basis. Thus, breeders, cat associations, and geneticists should develop stronger interactions on a more consistent basis to help maintain health cat populations.