Why is blood typing important in British Shorthair cats?
Blood typing is an important part of responsible British Shorthair breeding. Knowing the blood types of breeding cats allows breeders to plan matings more carefully and, above all, to reduce the risk of neonatal isoerythrolysis (NI) — a potentially life-threatening condition that can cause severe haemolytic anaemia and death in newborn kittens.
What blood types occur in cats?
The feline AB blood group system includes three main blood types:
- type A
- type B
- type AB, which is considerably less common.
The frequency of the different blood types varies between breeds and geographical populations. British Shorthairs are among the breeds in which type B occurs relatively frequently, making blood typing particularly relevant in breeding programmes.
Having blood type A or B is not, in itself, a health advantage or disadvantage. The importance of blood type becomes particularly apparent when planning certain breeding combinations.
Type B queen and type A tom — a mating requiring particular attention
The best-known risk occurs when a type B queen is mated to a type A tom.
If type A kittens are born from such a mating, they may be at risk of neonatal isoerythrolysis. Type B cats naturally have high levels of antibodies against type A red blood cells.
The kittens are born without signs of the disease. The problem begins after they start nursing. Through the first milk — colostrum — they absorb maternal antibodies. In a kitten carrying type A antigens, these antibodies can attack its red blood cells and cause haemolysis.
This condition is known as neonatal isoerythrolysis (NI).
The severity can vary considerably. Possible signs include:
- weakness,
- anaemia,
- jaundice,
- dark-coloured urine,
- poor nursing,
- necrosis of the tip of the tail,
- and, in severe cases, death during the first days of life.
Type AB kittens born to a type B queen may also be at risk, because their red blood cells also carry A antigen.
This is why knowing the parents’ blood types before mating, rather than only after the litter is born, is so important.
Type B queen and type B tom
From the point of view of neonatal isoerythrolysis, this is a compatible mating.
A type B cat has inherited B-associated variants from both parents. Therefore, when:
type B queen × type B tom
are mated, the kittens will also be type B.
There is consequently no situation in which a type B mother nurses type A or AB kittens, and the classical risk of neonatal isoerythrolysis associated with maternal anti-A antibodies is avoided.
For this reason, a type B breeding male may be particularly useful in a breeding programme that includes type B females.
What if the queen has blood type A?
The situation is different when a type B tom is mated to a type A queen.
This combination does not carry the classical risk of neonatal isoerythrolysis associated with a type B mother nursing kittens with type A antigen.
Type A cats may have naturally occurring antibodies against type B blood, but these antibodies are generally much weaker than the anti-A antibodies found in type B cats and have not been associated with the classical form of neonatal isoerythrolysis in type B kittens born to type A queens.
The blood types of the kittens will depend on the genetic variants carried by the parents.
A cat that is serologically identified as type A may carry a recessive variant associated with type B and can pass that variant on to its offspring.
This illustrates an important distinction between phenotype — the blood type identified by serological testing — and genotype — the genetic variants that a cat may pass on to its kittens.
What about a type AB queen?
Type AB is a separate and relatively rare feline blood type. It should not be understood simply as a combination of the A and B types.
Unlike type B cats, type AB cats do not have naturally occurring anti-A or anti-B antibodies. Therefore, a type AB queen does not present the classical neonatal isoerythrolysis risk associated with a type B queen.
However, because the genetics of feline blood groups are more complex than a simple A/B dominant–recessive model, genetic testing can provide useful additional information when planning breeding combinations.
Why can a type B tom be interesting in a breeding programme?
Blood type B can be a useful characteristic in a breeding male, particularly because it provides more options for safely planning matings with type B females.
In simplified terms:
| Queen’s blood type | Tom’s blood type | Typical NI risk associated with the A/B system |
|---|---|---|
| B | A | YES — requires particular attention |
| B | B | NO |
| A | B | NO |
A type B tom is not automatically a better breeding cat than a type A tom. Blood type is only one element in assessing a cat’s suitability for breeding.
Serological blood typing and genetic testing
It is important to distinguish between two types of information.
Serological blood typing tells us which blood type a cat actually has: A, B or AB.
Genetic testing can provide additional information about known genetic variants associated with blood type and may identify, for example, a type A cat that carries a recessive variant associated with type B.
This can be useful when planning future matings because two cats with the same serological blood type do not necessarily carry the same genetic variants.
Current DNA tests, however, do not detect every possible rare or unknown blood-group variant, so genetic results should not always be treated as a complete substitute for serological blood typing.
Blood type is only one part of a responsible breeding programme
The choice of a breeding pair should never be based on blood type alone.
Other important factors include:
- overall health,
- genetic test results,
- temperament,
- conformation and breed type,
- pedigree,
- degree of relatedness,
- and genetic diversity.
Blood typing is therefore one element of a much broader breeding strategy.
Why do we blood type our cats at Gotham?
At Gotham, we consider knowledge of our cats’ blood types to be one of the elements of conscious and responsible breeding planning.
It helps us select parents for future litters more carefully, anticipate the possible consequences of particular combinations and reduce avoidable risks to newborn kittens.
Good breeding does not begin when a litter is born. It begins much earlier — with knowledge of the cats, their ancestry, health and genetics, and with the careful selection of suitable parents for the next generation.