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HYBRID VIGOR for Maine Coon Cats
Article compliments of Furkats Maine Coon Cat Cattery
Published in Maine Coon International Issue 5: Winter 1995/6
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| Furkats W P Churchill, blue & white bicolor poly |
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Having once been a beef cattle farmer, I am familiar with the techniques and practices used in the beef cattle industry. In order to improve the quality of my cattle herd I became an artificial inseminator. In this way I was able to have a large selection of sires for my herd. One of the techniques we utilized was crossbreeding in order to achieve heterosis for various trait. (Definition of Terms) Heterosis according to Dr. Roy Burris (1995) is defined as the increase in productivity in the crossbred offspring above the average of breeds that are crossed. This means that offspring of a given mated pair will out perform their parents. When a Black Angus Bull is bred to a Hereford cow (red with a white face) the resulting offspring which is a black calf with a white face, is of higher quality for some traits than either of the parents. Burris (1995) defined crossbreeding as the mating of cattle of different breeds or breed compositions. He further stated that when crosses are made, one breed?s strengths can compliment the other's weaknesses. These same techniques of crossbreeding can be used to improve the vigor of our Maine Coon Cats. In cattle (Burris, 1995) the use of crossbreeding will increase the calving rate, livability and growth rate. An important point is that crossbreeding must be done with a long term plan. For this discussion the various UNRELATED LINES of Maine Coon Cats will be used to replace the term breeds. According to Dr. Bullock (1995) heterosis can also be expressed when two unrelated lines within a breed are crossed. These unrelated lines, for example, could be Heidi Ho, Dirigo or Choate. Personal cattery names will not work unless the cats used are totally unrelated. Most of the cats that are being used today are from the Heidi Ho Line. A planned breeding program would include using the various unrelated lines as an individual breed for the purposes of a crossbreeding schema. The following are examples of those plans:Two-Line Cross: Would represent a male form one unrelated line and a female from another, for example a Heidi Ho female bred to a Dirigo male. These kittens produces should demonstrate better characteristics than their parents. In this example the kittens would demonstrate hybrid vigor such as survivability, but the inbred parents would still result in relative low reproduction ratesThree-Line Cross: This could be done by breeding for example a Heidi Ho female to a Dirigo male, then saving a kitten. This kitten could be bred to a Choate cat. According to Burris (1995) this would provide for near maximum hybrid vigor. In other words, both parents and kittens would be outcrossed which should negate the adverse effects of inbreeding depression.Two-Line Rotation or Crisscross: A Simple crossbreeding system involving breeding two cats from different unrelated lines. For example a Heidi Ho male could be bred to a Choate female. In succeeding generations females are bred to sires that are of opposite lines from their sire. Two stud males from different lines are needed. These males would need to be replaced periodically.Three-Line Rotation or Crisscross: This plan would follow the same pattern as the two line rotation only a third line is added. This rotation maintains a higher level of hybrid vigor than that of a two-breeding system. Three distinct groups of cats are created and they are mated to the stud male which is least related to them.The above plans provide for maximum heterosis or hybrid vigor which will reduce the effects of inbreeding depression. Inbreeding depression according to Robinson (l988) is the term used to describe the decline in vigor or general weakness in purebred stock. It is produced because of an increasing number of genes that are homozygous (Robinson, 1988). This is because the genes are similar for most traits as opposed to being randomly mix as your would find in a natural population of animals (heterozygous). Robinson (1988) also stated that inbreeding depression may effect almost any feature or characteristic. This could include a decline in birth weight, lethargic kittens and poor growth rates. Litter size may be reduced with an increase in still born kittens or abnormal kittens. Robinson (1988) further noted that reproductive performance may fall off as evidenced by males failing copulate and females failing to come into heat. He also stated that there may be a greater incidence of illness, with cats being more delicate or temperamental which lead to an insidious condition when a majority of the animals within a bred are related. Our Maine Coons are becoming extremely homozygous. It is not uncommon for the same cat to be listed in pedigrees multiple times. Litter mate kittens are bred together then a kitten from that mating is bred back to an uncle then a kitten from that breeding bred back to one of the original mated pair. This has gone on for several generations. When will it stop? How may lethal characteristic will be uncovered before breeders realize that a homozygous gene pool is not a desirable state. In general, heterosis or hybrid vigor can be realized within a given breed of cats, if cats can be classified into unrelated genetic lines. With heterosis two different forms of a given gene are at a given locus on a chromosome (Siegal, 1990). According to Dr. D Bullock, 1995 the greatest effect of hybrid vigor is evidenced when two highly inbred lines are crossed. This happens because an extremely inbred line would be homozygous or have the same forms of a given genes at a given chromosome (Siegal, 1990). Isn't it time to practice some good animal husbandry and try using the principals of crossbreeding or outcrossing within a breed. This can best be accomplished by using the techniques already in practice by other groups of domestic animals. In summary, it is not necessary nor desirable to continue to line breed our Maine Coon Cat. Breeding programs are now at a point where continues inbreeding will continue to deepen the effect of inbreeding depression. Due to the phenomenon called hybrid vigor type and desired characteristic will not be lost. On the contrary outcrossing will only improve the strength of our beloved catsI would like to thank Dr. Bullocks for helping me with the technical parts of this article.
RESOURCESBullock, Darrh, Ph.D., Beef Cattle Extension Specialist Breeding and Genetics, Department of Animal Science, University of Kentucky, 1995.
Burris, Roy, Planning the Breeding Program ,Section 2, Beef Cow-Calf Management, University of Kentucky, Co-operative Extention Service, 1995, p.2.1 - 2-8.
Robinson, Roy, Genetics For Cat Breeders, New York:Pergamon Press, 1988, p.97-99.
Siegal, Mordecai, EDT., The Cornell Book of Cats, New York: Villard Books, 1990, p.391.
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