Animals have blood types, defined by the presence or absence of specific surface antigens on red blood cells. While the concept is universal, the systems vary widely from the human ABO classification. These inherited antigens determine how the immune system recognizes blood as “self” or “non-self,” and each animal group has evolved its own unique classifications.
Defining Animal Blood Group Systems
Animal blood groups rest on the diversity of red blood cell surface antigens. Unlike the standardized human system, animal blood group systems are highly varied. For example, cattle have at least 11 major blood group systems, with one system alone containing over 60 distinct factors, making matching complex.
Due to species-specific diversity, a blood type in one animal has no bearing on a blood type in another, even if they share a letter designation. Nomenclature often uses alphanumeric names to reflect the species and the identified antigen. Dogs use the Dog Erythrocyte Antigen (DEA) system, for instance, while cats use the Feline AB system. This standardized naming helps track the numerous, independently inherited antigens.
Blood Types in Common Companion Pets
The blood typing systems in dogs and cats contrast sharply in complexity and clinical risk. Dogs utilize the Dog Erythrocyte Antigen (DEA) system, which includes numerous groups. The DEA 1 antigen is the most clinically significant, with dogs being either DEA 1-positive or DEA 1-negative.
Dogs generally do not possess naturally occurring antibodies against other blood types. This means a DEA 1-negative dog can safely receive DEA 1-positive blood for a first transfusion. However, initial exposure causes the dog to rapidly produce antibodies, leading to a severe reaction if a second, incompatible transfusion is given later. Conversely, cats have a simpler Feline AB system, including Type A, Type B, and the rare Type AB.
Cats inherently possess strong antibodies against the blood type they lack, even without prior exposure. Type B cats have high levels of naturally occurring anti-A antibodies. Transfusing a Type B cat with Type A blood can cause a rapid, severe, and fatal hemolytic reaction. Type A cats typically have weaker anti-B antibodies, resulting in milder reactions if given Type B blood.
The Importance of Typing for Animal Health
Identifying an animal’s blood type is fundamental in modern veterinary medicine to ensure safe blood transfusions. Giving an incompatible blood type causes a life-threatening immune response where the recipient’s immune system attacks the transfused red blood cells. For cats, this risk is immediate due to pre-existing antibodies, making cross-matching necessary before any transfusion.
Blood typing is also important for managing Neonatal Isoerythrolysis (NI), a reproductive condition seen in foals and kittens. NI occurs when an offspring inherits a blood type from its father that differs from the mother’s. The mother’s antibodies, harmless to her, are passed to the newborn through the colostrum, where they attack the baby’s incompatible red blood cells.
In horses, NI frequently involves the Aa and Qa antigens; in cats, it occurs when a Type B mother is bred with a Type A or AB father. The condition causes the newborn to become severely anemic and jaundiced within hours of nursing, often resulting in death if not treated. Prevention relies on identifying parental blood types and preventing the newborn from nursing the colostrum for the first 24 hours.