|MadSci Network: Zoology|
Human blood groups are based on special proteins or antigens on the surface of the red blood cells. The most common blood type classification in humans is the A-B-O system. In addition to the antigens on the red cells, the body produces antibodies that react against the antigens on foreign red blood cells (as in a bad transfusion). In addition to the A-B-O system, there is also the Rh classification as well as many other potentially reactive antigens on the red blood cells.
Many animals have blood types too. For example, for dogs we use the canine erythrocyte antigen system (DEA)with 8 blood types. Each species has its own system with different antigens. I'm not sure if anyone has ever studied the blood types of deer, but I'm sure they have blood types too. But they would not have the same classification system as humans, so deer cannot have Type A blood, nor could you use deer blood for a human transfusion (there are a lot of other differences too - red blood cell size can vary between animal species).
Try the links in the MadSci Library for more information on Zoology.