Just like humans, cats have different blood types. It's good to know what type of blood Kitty has in case of a medical emergency. A blood transfusion could save his life one day, but only if he receives the right kind of blood.
Your kitty has one of three blood types: A, B or AB. His blood type depends on antigens on his red blood cells. If he has N-glycolyl-neurominic acid on his red blood cells, his blood type is A. N-acetyl-neurominic acid and his blood type is B. If he has both of these antigens on his red blood cells, he has the blood type AB. According to Cornell University College of Veterinary Medicine, 94 to 99 percent of mixed-breed cats in the United States have type A blood. Some breeds are more likely to have type B blood than others; some, like the Siamese, are universally type A. Your vet can do a blood test to determine your cat's blood type.
Kitty inherits his blood type from his mom and dad. The reason so many cats are type A is that A is the dominant blood type. If Kitty has one gene for A and one for B, he will be type A. If he has type B blood, both his parents were B as well. Type AB is determined by a different gene, and it extremely rare.
Kitty will naturally have antibodies to blood antigens that are different from his own, meaning his body will recognize them as foreign. Type A blood has low levels of antibodies towards type B blood, but type B blood has an extremely severe reaction to type A blood. If Kitty has type B blood and receives type A blood, his body will reject it and he will become very ill, and it could be fatal. If a B-type female breeds with an A-type male, the kittens will be type A. However, this combination can lead to neonatal isoerythrolysis, or NI—destruction of the kittens' red blood cells. The type A kittens get antibodies from their mother when they nurse, and mom has type B blood, so they will receive antibodies that attack their type A blood. NI can be fatal, so a type B queen should never be bred with a type A tom.
Type B Breeds
Some breeds are more likely to be type B than other breeds. The British shorthair, Cornish Rex and Devon Rex are three breeds with extremely high percentages of type B blood, up to 50 percent. Other breeds that have higher percentages of type B blood are Persians, Abyssinians, Somalis and Japanese bobtails. If you have one of these breeds of cats, its a good idea to have his blood tested before trying to breed him.