William R. Pritchard Veterinary Medical Teaching Hospital

Equine

Equine - Featured Services


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Equine Blood Typing
Horses have 8 different red blood cell groups or systems, which are named A, C, D, K, P, Q, U, and T. The first 7 systems are internationally recognized. Each system corresponds to a particular gene for which two or more alleles exists. The blood group genes produce surface molecules that contain antigenic sites known as factors. Over 30 different factors have been identified. The blood groups are named with an upper case letter to denote the system and a lower case letter to designate the factor (antigen). There are variable numbers of factors for each blood group. The VMTH Hematology laboratory types for the blood factors: A (a,b,c,f,g), Ca, D (a,g,k), Ka, P (a,b), Q (a,b,c), Ua, V, and W.

Blood typing is useful in selecting blood donor horses for transfusions and to determine mare/stallion compatibility before breeding to predict the potential for neonatal isoerythrolysis (NI). Historically blood typing has been used for parentage verification, but has been replaced by DNA typing.

Blood Transfusions
Whole blood transfusions are useful in the treatment of acute hemorrhage in the horse. At the UC Davis VMTH patients are blood typed and antibody screened to find an appropriate donor match prior to blood transfusion. We do not recommend whole blood transfusions without knowing the blood type of the recipient. Many veterinary laboratories are able to perform a simple hemagglutination crossmatch that should identify a large percentage of potential incompatibilities. The majority of horses lack naturally occurring antibodies, so a first whole blood transfusion is usually without consequence. Whenever a mare is given a whole blood transfusion, she is potentially being sensitized to blood group factors that may lead to NI problems in future foals.

Plasma Transfusions
Often a transfusion is needed to restore fluid loss or colloid replacement, but the red blood cells are not essential. In this case, a plasma transfusion may fulfill the clinical requirements. Plasma can be collected and stored frozen to administer when needed. Potential plasma donors should be positive for the blood factors Aa and Ca. Horses that are negative for these factors usually have naturally occurring antibodies (anti-Aa or anti-Ca) or may eventually develop these antibodies.

For either a potential whole blood or plasma donor a blood type and antibody screen is indicated.

Blood sample submission information (pdf)

Blood Factor Frequencies
  A system C system Q system U system K system

BRED

 Aa+ Aa- Ca+ Ca- Qa+ Qa- Ua+ Ua- Ka+ Ka-

Thoroughbred

 98% 2% 83% 17% 85% 15% 18% 82% 5% 95%

Arabian

 97% 3% 97% 3% 37% 63% 38% 62% 0% 100%

Standardbred

 81% 19% 83% 17% 1% 99% 46% 44% 54% 46%

Morgan

 81% 19% 90% 10% 1% 99% 46% 54% 1% 99%

Quarter Horse

 74% 26% 94% 6% 32% 68% 44% 56% 8% 92%

Paso Fino

 74% 26% 60% 40% 15% 85% 57% 43% 0% 100%

Peruvian Paso

 78% 22% 93% 7% 4% 96% 55% 45% 5% 95%

Tennessee Walking Horse

 70% 30% 93% 7% 3% 97% 88% 12% 4% 96%