The Feline Blood Type System
Cats have their own blood type system with three groups, known as A, B, and AB. Type A is the most common overall, but type B appears far more often in certain breeds, and AB is rare. A cat is born with its blood type for life, and it is determined by genetics rather than anything to do with its health. Because the frequency of type B varies so much between breeds, blood type matters most when you are planning matings.
Why a Mismatch Is Dangerous
The risk arises when a type B queen is mated to a type A tom and produces type A kittens. Her colostrum, the first milk, contains strong antibodies against type A blood, and when the kittens nurse they absorb these antibodies. The result can be neonatal isoerythrolysis, in which the mother's antibodies destroy the kittens' red blood cells, often causing them to fade and die within the first days of life. This is entirely preventable once you know the parents' blood types.
Test Before You Mate
The simplest safeguard is to blood type your breeding cats before you pair them, so you never unknowingly combine a type B queen with a type A tom. If such a pairing is unavoidable or planned, work with your veterinarian to protect the at-risk kittens, for example by preventing them from nursing on the queen for the first day or so. Individual kittens are rarely typed at birth, so new owners should not expect a blood type on their kitten's paperwork. Testing is quick, and it turns a hidden risk into a manageable plan.
Beyond Breeding Decisions
Blood type is not only a breeding concern, because it also matters if a cat ever needs a transfusion. Giving the wrong type in an emergency can trigger a severe and sometimes fatal reaction, so a known blood type can save time in a crisis. Owners can ask their veterinarian for a blood type test whenever it is useful, such as before surgery or other procedures. Recording each cat's blood type is a small step that protects both your kittens and your adult cats.