Blood Groups and Blood Transfusions in Horses

Last Updated on March 29, 2022 by Allison Price

The presence or absence certain proteins or sugars on the red blood cells membrane determines the blood group. There are many blood groups, and they vary from one domestic species to the next. Normally, people do not develop antibodies against the antigens in their red blood cells or other blood groups of that species. This is unless they have been exposed through a blood transfusion, pregnancy or blood transfusion. However, in horses or other species, antibodies that react to antigens from another person may be present without prior exposure. If the foetus is of a different blood type than the mare, the mare will produce antibodies against the antigens in her fetal red cells. The mare is exposed to the foreign antigen through the placenta. Foals that have the same foreign antigen from their stallion can have problems in future pregnancies. The mare will have high levels of the antibody which reacts against the foal’s blood type. The foals’ red blood cells can be destroyed by maternal antibodies transmitted in colostrum (first breast milk). Because the foal’s first foal is born with this blood type, the mare has not had the time to make the antibodies. This immune disorder is called neonatal Ioerythrolysis.

Blood Groups and Blood Transfusions in Horses

There are eight major blood groups in horses: A, B, C and D, K and P. Q, U and T seem to be most likely to trigger an antibody response in horses if they are given to horses that are negative for them. These groups are used to match blood donors and recipients, and to identify breeding partners at risk for neonatal isoerythrolysis. These systems can also be used to confirm horse pedigrees because blood group antigen expression is genetically controlled. In most cases, however DNA testing has replaced blood typing in paternity testing.

Blood typing

Blood typing is the process of testing an animal’s blood for antibodies by taking a small amount of blood and measuring its reaction to them. It is best to identify potential donors for horses in advance. This is because it is difficult to find recipients in an emergency. It is possible to minimize the chance of transfusion reactions by selecting donors who are not susceptible to the blood group antigens A, C, and Q. A crossmatch is an additional test that compares donor red blood cells and plasma from the recipient. This allows for identification of possible reactions prior to transfusions or breeding.

Blood Transfusions

A blood transfusion may be necessary in an emergency situation such as bleeding from a wound or the sudden death of red blood cells. Long-term anemia may also require transfusions. Repeated transfusions are often required for animals with blood clotting problems.

Because blood transfusions can cause adverse reactions in some cases, it is important to take care. Transfusions that cause immediate destruction of red cells are the most dangerous. Horses are not able to match completely, and red blood cells can survive for only 2 to 4 days even if the recipient and donor are compatible. Fever and the spread infection are two other possible complications.