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Blood Type Incompatibility in Cats

Reviewed by Urs Giger PD Dr.Med.Vet. M.S. F.V.H.
Chief of Section of Medical Genetics, University of Pennsylvania

The genetics of the A and B blood types in cats is not the same as the A/B/O system in humans. There are three feline blood types:

  • Type A
  • Type B
  • Type AB (rare)
Blood groups in cats are inherited as a simple autosomal trait. Blood type A is dominant over type B. Most cats are Blood type A and about one-third of those have naturally occurring, low-titered, anti-B antibody.... meaning their blood contains an antibody that attacks Type B blood cells.

Type B cats all have a naturally occurring, highly titered anti-A antibody.

In the United States, the percentage of cats with the Type B blood varies from 0.3% to 59% depending on the breed. 95% of all domestic mixed breed cats in the United States are Type A. In pedigreed cats, the frequency of Type B blood varies greatly from breed to breed. Some breeds have no known Type B individuals, while half of some breed's numbers are Type B.

Obviously, the issue of blood type incompatibility can be a major concern for fanciers of many breeds.

Basically, Type A blood is incompatible with Type B blood.

There are two major risks resulting blood incompatibility:

  • Mating Risks
  • Transfusion Risks

Mating Risks
Blood Type Incompatibility becomes significant to cat breeders because Type A is dominant over Type B. That means that most of the offspring of a Type B female bred to a Type A male will usually have Type A blood. A high percentage of these kittens will often die suddenly after nursing in what is known as Neonatal Isoerythrolysis ("NI") or hemolysis of the newborn.

When the Type A kittens nurse from their Type B mother, anti-A antibodies in the colostrum and first milk of the Type B mother will cause rapid destruction of red blood cells in her kittens.

The kittens appear healthy and vigorous at birth, but some kittens suddenly die after nursing while others fade and die within the first week. The fading kittens stop nursing and may become pale or jaundiced due to the destruction of their red blood cells. They often have reddish urine.

The RED URINE distinguishes NI from other causes of Fading Kitten Syndrome.

Breeders should check all kittens for red urine during the first 2 days of life. NI can occur in the queen's very first litter, as well as subsequent litters and affect one or all of her kittens in a litter.

The diagnosis of Nl is confirmed by blood typing the stud and the queen, or the queen and kittens. Typing of the kittens would be difficult once they've died.

Other Causes of Early Kitten Mortality
Of course, not all early kittens losses are due to blood incompatibility. Other causes include:

  • infections such as G Strep, septicemia or pneumonia
  • maternal neglect
  • lack of colostrum
  • improper supplementation
  • metabolic abnormalities
  • immune deficiency
  • poor environmental conditions

Treatment of Kittens with Neonatal Isoerythrolysis Blood Incompatibility

  • Once the symptoms of NI are noticed, some kittens may be saved by a transfusion of red blood cells from the queen. It is however, very difficult to save these kittens.
  • Surviving kittens usually recover to full health but may develop necrosis of the tail tip at 2 weeks of age.

If You Know Your Type B Queen has been Bred to a Type A Male:

  • remove the kittens at birth prior to nursing.
  • Foster them on a Type A queen or hand-rear them on artificial milk for 1-2 days.
  • After 2 days, the kittens may be safely returned to the queen since anti-A antibodies in the milk can no longer be absorbed by the intestines of the kittens.

Cats at Risk

  • Devon Rex, British Shorthair, and Cornish Rex breeds
  • Queens with a history of high kitten deaths should be blood typed to rule out incompatibility issues.

Transfusion Reactions
Cats with the relatively rare Type B blood can die if they are given a transfusion with the common Type A blood and vice versa. If cats are transfused, even once, with an incompatible blood type, a Hemolytic Transfusion Reaction ("HTR") will occur and death is extremely likely. In general, you don't know a cat needs a transfusion (to treat a blood disorder or trauma) until it's an emergency.

Blood Typing
In any breed with Type B cats, the queen, the queen and the stud should be typed before breeding in order to make sure they are both of compatible blood type. The blood type does not change, so a cat only needs to be typed once.

A quick, easy and inexpensive test is available for determining your cat's blood type. For complete details on this procedure, please read the PandEcats article titled, Blood Type Testing Your Cat

To Avoid Problems of Blood Type Incompatibility

  • Blood type all cats and avoid mismatched matings of Type A or AB studs with Type B queens. If such a breeding occurs, the kittens should not be allowed to nurse from their mother for 18-48 hours, after which time the maternal antibodies will no longer be absorbed by the kitten.
  • Breeders may elect to eliminate Type B queens from the breeding pool and have only Type A queens and kittens in their breeding program.
  • The only safe breeding for a Type B female is to a Type B male. If the Type B queen is of top show quality, then mating her with a Type B stud would be the ideal solution. This, however, will ultimately result in more B Type kittens in your cattery which will grow up into Type B queens that when mated with a Type A stud could produce kittens with neonatal erythrolysis. It is a Catch-22.

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Reprinted with permission of ShowCatsOnline.com/PandEcats.com

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