Blood groups are determined by genetically controlled, polymorphic, antigenic components of the RBC membrane. The allelic products of a particular genetic locus are classified as a blood group system. Some of these systems are highly complex, with many alleles defined at a locus; others consist of a single defined antigen. Blood group systems, in general, are independent of each other, and their inheritance conforms to Mendelian dominance. For polymorphic blood group systems, an animal inherits one allele from each parent and thus expresses no more than two blood group antigens of a system. An exception is in cattle, in which multiple alleles are inherited.
Normally, an individual does not have antibodies against antigens present on its own or against other blood group antigens of that species’ systems unless they have been induced by transfusion, pregnancy, or immunization. In some species (people, sheep, cattle, pigs, horses, cats, and dogs), so-called “naturally occurring” isoantibodies, not induced by transfusion or pregnancy, may be present in variable but detectable titers. For example, Group B cats have naturally occurring anti-A antibody.
Also, circulating antibodies to animal blood group antigens may be induced by transfusion. With random blood transfusions in dogs, there is a 30%–40% chance of sensitization of the recipient, primarily to blood group antigen DEA 1, but risk is also present for development of antibody to any other antigen lacked by the recipient. In horses, transplacental immunization of the mare by an incompatible fetal antigen inherited from the sire may occur. Immunization also may result when some homologous blood products are used as vaccines (eg, anaplasmosis Anaplasmosis Anaplasmosis, formerly known as gall sickness, traditionally refers to a disease of ruminants caused by obligate intraerythrocytic bacteria of the order Rickettsiales, family Anaplasmataceae... read more in cattle). In dogs, prior pregnancy does not result in sensitization of the bitch to foreign blood group antigens.
The number of major recognized blood group systems (see Table: Major Blood Groups of Clinical Interest Major Blood Groups of Clinical Interest Blood groups are determined by genetically controlled, polymorphic, antigenic components of the RBC membrane. The allelic products of a particular genetic locus are classified as a blood group... read more ) varies among domestic species, with cattle being the most complex and cats the simplest. Animal blood groups are typed to aid in the matching of donors and recipients and, especially in horses, to identify breeding pairs potentially at risk of causing hemolytic disease in their offspring. Because expression of blood group antigens is genetically controlled and the modes of inheritance are understood, these systems also have been used to substantiate pedigrees in cattle and horses; however, in most cases, DNA testing has replaced blood typing for paternity testing.
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Also see pet health information regarding blood groups and blood transfusions in dogs Blood Groups and Blood Transfusions in Dogs Blood groups are determined by the presence or absence of certain antigens (proteins and sugars) on the red blood cell membrane. Normally dogs do not have antibodies against any of the antigens... read more , cats Blood Groups and Blood Transfusions in Cats Blood groups are determined by the presence or absence of certain antigens (proteins or sugars) found on the red blood cell membrane. The number of blood group systems varies among domestic... read more , and horses Blood Groups and Blood Transfusions in Horses Blood groups are determined by the presence or absence of certain proteins or sugars found on the red blood cell membrane. The number of blood groups varies among domestic species. Normally... read more .