In man blood group is applied to single factor. This factor is agglutinogen and is also called antigen. It is found on the surface of red blood corpuscles.

Accordingly a person with `A' antigen is designated as a person with A-group, with `B' antigen as B-group, with both A and B antigens as AB-blood group and a person without any antigens is designated as O-blood group.

In the case of animals blood group is applied to combinations of blood factors. So it is preferable to call it as blood group systems rather then blood groups. Each system has many factors, which are together called blood group factors.

Dr. J. Moustgaard, of the Royal Veterinary & Agricultural College, Copenhagen has identified in cattle ten group systems namely A,B,C,FV,J,L,M,SU, Z and R'S'. Except J and L, all the other group systems have more than one group factor. For example the group factors of the group system A are designated as A{-1}, A{-2}, D, H, Z'.

The grouping factors are particular serum proteins. Acquiring of each protein is an inherited character. So examination of blood sample from within a breed might eventually prove a very useful means of selection. It might also indicate what mating could be expected to result in infertility.

The B-group system only has greater number of grouping factors. It has nearly 27 group factors, which are called phenogroups. Some of these are unique to particular breeds.

They are particularly valuable in determining incorrectly stated parentage. In dogs serum major groups have been recognised in the USA and they are referred to as A to G.

In veterinary practice blood transfusion is used in cases of haemorrhage and shock and to a lesser extent as part of the treatment of certain infectious diseases.

In cattle the donor and recipient are usually in the same herd. This fact lessens the risk of introducing infection and incompatibility does not arise.

But normal antibodies against the blood group factor-J are sometimes found in cattle. Thus if the donor's blood is J-positive and the recipient's blood contains normal antibody called anti-J the so-called transfusion reaction might be expected immediately following blood transfusion. These reactions are dyspnoea, muscular twisting, increased salivation and circulatory disturbances.









However, if an animal has been exposed to repeated blood transfusions, a different situation will arise. The animal will now have formed antibodies against the blood group antigens it does not have itself. It is therefore by no means unlikely that the blood of donor and the recipient are incompatible.

If this is so, transfusion will set off strong transfusion reactions. Such reaction can occur on the second or on subsequent blood transfusion.