Type B Blood in Cats

Cats have three blood types---A, B and the extremely rare and not yet fully understood AB. Inherited independently, AB was first described in the 1960s and appears to be recessive to the A gene but dominant to B. B group cats have special problems, mostly associated with breeding.

  1. Inheritance And Testing

    • Blood type is inherited. Kittens receive one gene from each parent, either an A or B. A is the dominant gene and always expressed. Consequently, cats with B blood type must have two B genes. Blood tests reveal phenotype (observable trait) but not genotype (actual genetic makeup behind the trait). Therefore, there is no way to tell if an A blood type cat has two A genes or an A and a B.

    Blood Transfusions

    • Unlike humans, cats have no universally compatible blood type so testing is important prior to transfusion. All cats have antibodies that will attack foreign blood. Group A cats have relatively low anti-B antibodies so can tolerate receiving some B blood, for example Group A blood carrying the recessive B gene. Type B cats, on the other hand, can die almost instantly from receiving type A blood.

    Blood Group Incompatibility

    • The biggest problem associated with B blood is Blood Group Incompatibility (BGI) or "Fading Kitten Syndrome." Also known as neonatal isoerythrolysis, it occurs when type A kittens are born to a type B mother. Through her colostrum (first milk), her anti-A antibodies attack the kittens' red blood cells, usually causing death. Surviving kittens are jaundiced, pass brownish-red urine and may lose the tips of their tails.

    Treatment Of Kittens

    • If BGI is recognized within the first few hours, affected kittens are removed from the mother. They may be given type B blood transfusions of "washed" cells which won't be destroyed by the mother's anti-A antibodies. Generally, BGI is detected too late and there are practical difficulties in transfusing newborn kittens.

    BGI Prevention

    • One option is to stop breeding group B cats. This limits choice of animals and is practical only in breeds where type B is rare. Secondly, it's possible to only mate group B queens (females) with group B toms (males). Notably, this eventually increases the proportion of group B cats in the breed. Finally, kittens can be hand-fed for their first day or so, preventing them suckling colostrum from their Group A mother.

    Breeding Considerations

    • Blood type must be taken into consideration when breeding purebreds, crossing different breeds, using random-bred cats to create new breeds, and when hybridizing domestics with wild species, where different blood type incidence is not yet known. A highly desirable outcross cat may introduce coveted traits but may also introduce unwanted blood type.

    "B" Cat Breeds

    • Certain breeds are type A only, including Siamese, Burmese, Tonkinse and Russian Blue. Others, like the Maine Coon, Ragdoll, and random-bred domestic, exhibit low B frequency, from 1 to 10 per cent. The Abyssinian, Himalayan, Persian, Sphinx and Scottish Fold have up to 20 per cent B frequency while the Cornish and Devon Rex have up to 50 per cent chance of having type B blood. Statistics vary from country to country.