BLOOD GROUP INCOMPATIBILITY IN CATS

For all practical purposes, cats are considered to have two blood groups: A and B. The third blood group, AB, is very rare in cats. As with humans, when giving a transfusion, the blood groups must be matched otherwise the cat's antibodies will destroy the alien blood cells.

Blood group incompatibility (BGI) can present a problem to breeders. One of the causes of Fading Kitten Syndrome is "neonatal isoerythrolysis". This means the kittens have a different blood type from their mother and the antibodies in her milk attack those kittens' red blood cells. The symptoms are jaundice, brown urine and rapid deterioration and death. In less severe cases, the affected kitten's tail-tip drops off. The diagnosis is confirmed by blood-typing the mother and affected kittens.

In controlled breeding programmes, BGI can be prevented by blood-typing the parents before mating them. Kittens receive one blood-type gene from each parent. Blood-type A genes are a dominant to blood-type B genes and the trait is autosomal (non-sex-linked).

BLOOD TYPES AND CARRIERS

A cat may be blood-type A but still carry the recessive gene for blood-type B. If two carriers of blood-type B are bred together, there is a probability of some kittens being blood type B.

* A cat homozygous (pure-breeding) for type A has 2 matching "A" genes
* A cat heterozygous for type A (carrier of type B) has one dominant "A" gene and one recessive "b" gene.
* A cat homozygous (pure-breeding) for type B has 2 matching "b" genes.

* A cat with type A phenotype may have the genotype AA (homozygous i.e. non-carrier) or the genotype Ab (heterozygous i.e. carrier).
* A cat with type B phenotype can only be genotype bb (homozygous).

The inheritance and full implications of the rare AB blood type is not yet understood. Note that "Ab" means a blood-type A cat carrying the recessive "b" gene and is different from a blood-type "AB" cat. Blood type B is shown by upper case "B". The recessive gene for that blood type is shown by lower case "b".

HOW BLOOD GROUPS ARE INHERITED

Problems occur when 2 carriers of type B are bred together and a type A female gives birth to type B kittens.

 

This table explains the different genotypes Ab and bb. Carriers are shown in shaded orange cells. Type B are shown in shaded red cells. AA and bb (pure-breeding for their blood group) are shown in shaded green cells. In subsequent tables, only the genotype and shading will be given.

 

Type B Parent

 

 

Type B Parent

Type A Parent

b

b

 

Type A parent carrying type B

b

b

A

Ab

Type A, carrying type B

Ab

Type A, carrying type B

 

A

Ab

Type A, carrying type B

Ab

Type A, carrying type B

A

Ab

Type A, carrying type B

Ab

Type A, carrying type B

 

b

bb

Type B

bb

Type B

 

DIFFERENT MATINGS BETWEEN TYPE A AND TYPE B CATS

Mating together 2 cats with "AA" produces type A kittens.

 

Type AA parent

Type AA parent

A

A

A

AA

AA

A

AA

AA

 


Mating together 2 cats with "bb" produces type B kittens.

 

Type B parent

Type B parent

b

b

b

bb

bb

b

bb

bb

 

While it is easy to test for type B, it is harder to find out whether a type A cat is "AA" or "Ab" because current tests cannot show whether he is a type B carrier. The only way to find out is to test mate him to a known type B female.

 

Type B Female

 

 

Type B Female

Type AA Male

b

B

 

Type Ab Male

b

b

A

Ab

Ab

 

A

Ab

Ab

A

Ab

Ab

 

b

bb

bb

 

If the type A cat is a carrier, then half of the kittens produced with a type B female will show signs of BGI. If he isn't a carrier, then none of the kittens will be at risk, but they will all be known carriers of type B. However, and it is a big however, due to the random way genes are passed on, it may take several matings to completely rule him out as a carrier.

 

Type Ab Female

Type Ab Male

A

b

A

Ab

Ab

b

Ab

bb

 

When 2 carriers are mated together, on average one quarter of all kittens will be type B. Because type Ab queens have less anti-B antibodies than type AA queens, some of those kittens might survive. However, the queen will build up antibodies as a result of having type B kittens, and if she has type B kittens in the future, they are more likely to develop full-scale neonatal isoerythrolysis and die. The only way to tell whether a queen is AA or Ab is to test mate her to a type B male

.

 

Type AA Female

 

 

Type Ab Female

Type B Male

A

A

 

Type B Male

A

b

b

Ab

Ab

 

b

Ab

bb

b

Ab

Ab

 

b

Ab

bb

 

Once again, if she carries the recessive type B gene, on average half of her kittens sired by a type B male will be type B and will show signs of BGI. If mated to a type Ab male, one quarter of kittens are likely to have BGI.

 

Type Ab Female

Type Ab Male

A

b

A

Ab

Ab

b

Ab

bb

 

PREVALENCE OF TYPES A, B AND AB IN DIFFERENT BREEDS

Some breeds are more likely than others to have type B. This may be because the foundation cats, purely by chance, didn't have the recessive "b" gene or it may be that the recessive "b" gene has been bred out of the gene pool (recessive genes are notoriously hard to eradicate as they can be carried undetected for many generations before meeting up with another carrier). 

Type B frequency

BREEDS
(Due to different gene pools, frequency within breeds differs between USA, UK/Europe and Australia)

None

Siamese and related breeds, Burmese, Tonkinese, Russian Blue

1-10%

Maine Coon, Norwegian Forest Cat, Ragdoll, random-bred domestic cats

11-20%

Abyssinian, Birman, Himalayan, Persian, Somali, Sphinx, Scottish Fold, Japanese Bobtail

21-50%

Exotic Shorthair, British Shorthair, Cornish Rex, Devon Rex

Type AB

 

 

Scottish Fold, Birman, British Shorthair, Somali, Bengal, Abyssinian, Ragdoll, random-bred domestic cats

 

The blood type is an additional consideration when outcrossing cats to broaden or reinvigorate a gene pool. Will the outcross cat introduce type B into a breed that previously had no incidence of type B? The same applies when hybridising cats (different blood type incidence in wild species is not yet known) or crossing different breeds or using random-bred cats to create new breeds. A highly desirable outcross cat may introduce the required traits, but may also introduce an unwanted blood type.

BLOOD-TYPING KITTENS

Kittens can be blood-typed at birth using a drop of blood from the umbilicus. If the kitten is the same blood type as the mother, it is safe for it to suckle from her. If the blood types differ, it is advisable that the kitten does not suckle from her for its first 16 hours of life as that is when its gut is permeable enough to allow antibodies from her colostrum to get into the bloodstream. Since maternal antibodies are important during the kitten's early life, hyperimmunoglobulin sera is available for kittens that are hand-reared due to Blood Group Incompatibility. After 16 hours it is considered safe to allow it to suckle from their mother.

TRANSFUSIONS

Because there is no type O in cats, there is no universal donor. If cats receive the wrong blood type even once, a Haemolytic Transfusion Reaction occurs and can result in death. For this reason, it is sensible to know a cat's blood type, especially if it is a breed with a high incidence of type B. Usually a cat will only need a transfusion due to an emergency (blood disorder or traumatic accident) and any delay while ascertaining its blood type could be life threatening. Giving the wrong blood type is equally life-threatening.

In recipient cats given correctly matched blood, the transfused (donor) red cells survive for about 35 days. Incompatible blood cells are destroyed within 7 days.

Type B cats can die if they receive a blood transfusion containing the more common type A blood. Type B cats have medium to high levels of anti-A alloantibodies which causes the rapid destruction of transfused type A red cells. This can occur within hours and there is a high risk of anaphylactic shock.

If a type A cat receives type B blood, an immediate transfusion reaction is unlikely to occur as type A cats have relatively low levels of Anti-B alloantibodies. However the type B red cells will have a greatly reduced lifespan.

Type AB cats are rare. Ideally, they should receive blood from a type A donor. They can receive type B blood, but as type AB cats potentially have Anti-B alloantibodies, this may result in premature destruction of the type B red cells in donated blood.

MESSYBEAST : NEUTERING & MEDICAL