Understanding Type B Blood in Cats: Genetics, Risks, and Breeding Considerations

Introduction

Blood type might not be the first thing cat owners think of when it comes to feline health or breeding, but it plays a crucial role—especially in medical situations and breeding decisions. While most people are familiar with human blood types like A, B, AB, and O, cats have their own blood group system, which functions differently. Among these, type B blood is less common but vitally important to understand due to its impact on transfusions, neonatal isoerythrolysis (NI), and breeding programs.

This article explores the genetics, distribution, health implications, and breeding considerations surrounding type B blood in cats. We’ll also look at why knowing your cat’s blood type can mean the difference between life and death—and how responsible breeding can help prevent tragic outcomes.

  1. Feline Blood Groups: An Overview

Cats have a three-type blood group system: A, B, and AB.

  • Type A: The most common blood type worldwide. Cats with type A blood may have weak anti-B antibodies.
  • Type B: Less common; cats with this type have strong anti-A antibodies.
  • Type AB: Very rare; these cats have no naturally occurring antibodies and can receive A or B blood.

Unlike in humans, cats naturally develop antibodies against the blood types they do not have, even without prior transfusions. This makes blood type compatibility crucial in transfusions and reproduction.

  1. Type B Blood: What Does It Mean?

A cat with type B blood has B antigens on the surface of its red blood cells and anti-A antibodies in its plasma. These antibodies are strongly hemolytic, meaning they will attack and destroy any type A red blood cells introduced into the body.

Key facts about type B cats:

  • They can only receive blood from other type B cats.
  • They will have a severe transfusion reaction if given type A blood.
  • Female type B cats bred with type A or AB males are at high risk of producing kittens with neonatal isoerythrolysis (NI), a fatal condition for newborns.

Understanding a cat’s blood type is essential to preventing these risks, especially in breeding and veterinary medicine.

  1. Genetics of Type B Blood in Cats

Blood type in cats is determined by a single gene with multiple alleles on chromosome B2, known as the AB blood group system. The primary alleles involved are:

  • A – Dominant
  • b – Recessive
  • ab – Rare variant (co-dominant or recessive depending on context)

Possible Genotypes and Phenotypes:

Genotype Phenotype (Blood Type)
AA Type A
Ab Type A (carrier of B)
bb Type B
ab Type AB
Aa/ab Type A or AB (varies)

A cat must inherit two copies of the b allele (bb) to be type B. This makes type B cats homozygous recessive.

Inheritance Pattern:

The inheritance follows Mendelian recessive rules:

  • If two type A carriers (Ab) mate, 25% of kittens may be type B.
  • If one parent is type B (bb) and the other is a carrier (Ab), 50% of kittens may be type B.
  1. Distribution of Type B Blood Among Cat Breeds

The prevalence of blood types varies significantly by breed and geography.

High Type B Frequency Breeds:

  • British Shorthair
  • Devon Rex
  • Cornish Rex
  • Exotic Shorthair
  • Persian
  • Himalayan
  • Turkish Van and Turkish Angora
  • Birman
  • Scottish Fold

In some of these breeds, up to 40–60% of individuals may have type B blood.

Geographic Influence:

  • Type B is more common in parts of Australia, the UK, and parts of Europe.
  • In the U.S., type A dominates in most breeds, but pockets of high B prevalence exist in some breeds and regions.
  1. Health Implications of Type B Blood
  2. Transfusion Reactions

A type B cat given type A blood will almost certainly experience a life-threatening acute hemolytic transfusion reaction due to naturally occurring anti-A antibodies.

Symptoms of a mismatched transfusion include:

  • Fever
  • Vomiting
  • Collapse
  • Hemoglobinuria (blood in urine)
  • Death (in severe cases)
  1. Neonatal Isoerythrolysis (NI)

NI occurs when:

  1. A type B queen mates with a type A or AB tom.
  2. Some kittens inherit the type A blood.
  3. These kittens ingest colostrum containing strong anti-A antibodies in the first 24 hours after birth.

The antibodies attack the kittens’ red blood cells, causing hemolysis.

Symptoms in Affected Kittens:

  • Failure to thrive
  • Jaundice
  • Dark red/brown urine
  • Anemia
  • Death within the first few days

NI is preventable with blood typing and proper breeding practices.

  1. Blood Typing: Testing and Methods

Knowing your cat’s blood type is critical in emergencies and breeding.

Testing Methods:

  1. In-Clinic Blood Typing Kits
  • Provide rapid results (10–20 minutes)
  • Use a small blood sample
  • Examples: RapidVet-H, Card Agglutination Tests
  1. Laboratory Testing
  • More comprehensive and reliable
  • May include genotyping to detect carriers
  • Offered by labs like UC Davis, Langford Vets, Wisdom Panel

When to Test:

  • Before breeding
  • Before any surgery or blood transfusion
  • If you own a breed with high B prevalence
  • When adopting or rescuing unknown pedigree cats
  1. Breeding Considerations for Type B Cats

Breeding cats without knowing their blood types can lead to devastating consequences, especially when type B cats are involved.

  1. Avoiding NI

Never mate a type B queen with a type A or AB tom without taking precautions. If mating must occur:

  • Prevent kittens from nursing for the first 24 hours.
  • Provide a safe colostrum alternative.
  • Blood type kittens immediately after birth.
  1. Ideal Breeding Pairings:
Queen Type Tom Type Risk of NI Recommendations
B B None Safe
B A/AB High Avoid or manage
A/AB B None (but offspring may be B) Screen kittens

Breeders should use genotyping to determine carrier status and plan matings accordingly.

  1. Breeding Ethics

Breeders should:

  • Test all breeding cats for blood type and disease.
  • Avoid producing high-risk pairings.
  • Be transparent with buyers about kittens’ health and blood type.
  • Work to reduce the incidence of preventable conditions like NI.
  1. The Rare Type AB Blood in Cats

While type B is uncommon, type AB is extremely rare and genetically not well understood. Cats with AB blood:

  • Have both A and B antigens.
  • Do not have naturally occurring antibodies, making them universal plasma recipients.
  • Can receive blood from type A, B, or AB donors (though best matched with AB).

Their genetic makeup may involve co-dominance or a separate allele, possibly designated a^ab. Further research is ongoing.

Breeders encountering AB cats should report occurrences and consult feline geneticists.

  1. Type B and Blood Banking

Type B cats are in high demand as blood donors—especially in emergency clinics and feline blood banks. However:

  • Most blood banks require healthy, calm cats over 10 lbs and 1–8 years old.
  • Donors are tested for FeLV, FIV, and other infections.
  • Blood is stored with anticoagulants and matched to recipients with typing and crossmatching.

Having typed feline donors of all blood types, especially B and AB, is critical for veterinary care.

  1. The Future: Genetic Testing and Breed Preservation

As genetic testing becomes more affordable, breeders can now screen for both blood type phenotype and genotype. This helps identify:

  • Carriers of the b allele in type A cats.
  • Ideal breeding pairs to avoid type B complications.
  • Individuals with rare or unusual blood profiles (e.g., Mik antigen variants).

Programs like the 99 Lives Cat Genome Project are helping scientists understand blood group genetics on a molecular level, which could lead to better tools for screening and breeding.

Conclusion

Type B blood in cats may be less common, but it has a disproportionate impact on feline health, especially in the context of breeding and transfusions. Understanding the genetics behind blood type

, testing all cats before breeding, and avoiding high-risk pairings can prevent neonatal deaths and transfusion tragedies.

Breeders, veterinarians, and cat owners alike have a shared responsibility to promote safe practices around feline blood type. As testing becomes more accessible and awareness grows, we move toward a future where preventable conditions like neonatal isoerythrolysis are virtually eliminated.

Key Takeaways

  • Type B cats have strong anti-A antibodies and can only safely receive type B blood.
  • The bb genotype causes type B blood and follows a recessive inheritance pattern.
  • Breeding type B queens with type A/AB males risks neonatal isoerythrolysis (NI).
  • Blood typing and genotyping are critical tools for safe breeding and veterinary care.
  • Responsible breeding can prevent suffering and contribute to healthier feline populations.

 

 

Mating of a male in blood group A with a female in blood group B

Here are the theoretical results obtained by mating males in blood group A (alleles A/A, A/aAB or even A/b) with a female in blood group B (alleles b/b). This demonstrates the importance of having parents genetically tested before mating them.

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