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Above two cornish rex variant kittens.

Outcrossing -

In the UK, to expand the small Cornish Rex gene pool, we are allowed to outcross, to a number of other breeds (GCCF rules).

The Approved list of breeds, include the Abysinian, Asian Shorthair, British Shorthair, Burmese, Oriental Shorthair, Russian Blue and the Siamese.

In my breeding program, I have used cats with British Shorthair, Oriental Shorthair and Russian Blue outcrosses.

Cornish Rex and Devon Rex genes are not compatible, and any mating between the two, is highly undesirable. Kittens of any such mating, will be registered on the Reference Register, and not considered to be Variants. They cannot be used in either a Cornish or Devon breeding programme.


When undertaking an outcross, it is best to know, the blood group of both cats.

In cats, there are 3 blood groups, A, B, and AB. Blood group A is dominant to blood group Ab and B, and Ab is recessive to blood group A, but dominant to B.  Blood group A (dominant) produces no antibodies, or very weak ones, to blood group  B.  Blood group AB cats produce no antibodies, against either of the other blood groups. Blood group B produces powerful antibodies to blood group A, and these anti-A antibodies can cause serious problems.

Cornish Rex x Lilac Colourpoint British Shorthair. Photograph taken days before the queen gave birth to 1 black male, and 3 red females. Kittens' photos above.

Burmese, Orientals, Russian Blues, Siamese are exclusively type 'A', and approximately 60% of British Shorthair are group 'B'.


If you are planning to breed from your blood group 'B' queen, the stud's blood  group, is very important.  A blood group 'B' queen mated to a blood group 'B' stud, will only  produce blood group 'B' kittens,  and there is no risk of incompatibility. However  if a blood group 'A' stud, is mated to a blood group 'B' queen, the possibility of the queen giving birth to blood group 'A' kittens exists.  All of these kittens are at risk of developing Isoerethrolysis, if allowed to suckle from their  mum, in their first 24 hours of life.

Fortunately, the kittens are only at risk, from the effects of the maternal antibodies, for about their first 16-24 hours of life. Then the kittens gut lining becomes impermeable, and the maternal antibodies are unable to pass across it, into their blood stream, and cause damage. It is then safe for blood group A kittens, to be returned to feed from their blood group 'B' mum.

Recent research suggests that the critical period, for keeping kittens, from their mum may be as little as 16 hours. To be on the safe side, it is advisable to keep them away 24 hours.

For professional advice on blood groups, and ways of keeping your kittens safe from developing Isoerethrolysis, please visit Dr. Diane Addie's site.

Feline Blood Groups

Information on A and B Blood groups, a must for anyone about to undertake outcrossing. Written by Dr. Diane Addie, who is based at Glasgow University.

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