5th on 21 interesting Facts About Dogs: Dogs have 13 blood types, horses have 8, cows have 9 while Humans only have 4.
Over 13 canine blood groups have been described. Eight DEA (Dog Erythrocyte Antigen) types are recognized as international standards. Of these DEA types, DEA 4 and DEA 6 appear on the red blood cells of ~98% of dogs. Dogs with only DEA 4 or DEA 6 can thus serve as blood donors for the majority of the canine population. Any of these DEA types may stimulate an immune response in a recipient of a blood transfusion, but reactions to DEA 1.1+ are the most severe.