Dr. C. Baldwin, BVetMed, MRCVS of Sussex Equine Hospital explains about blood transfusions in horses, why they are so much more complicated than human transfusions and how there is a one in a half a million chance of an exact match…
Blood and plasma are vital fluid therapies for horses and foals. Unfortunately, there are no blood banks for horses (as there are for humans and some small animals) because horse red blood cells do not store well. Blood can only be drawn from a donor horse when a transfusion is needed.
In general blood transfusions are used to supply either plasma or whole blood. This article will discuss both and will also outline the ideal characteristics of a horse blood donor. Before this is discussed it is important to understand how blood is divided. Blood can be broadly divided into two parts; plasma and red blood cells. The plasma contains the white blood cells and antibodies effective in fighting infections. The plasma also contains large proteins and clotting factors that help the blood clot when bleeding occurs. The red blood cells deliver oxygen to the rest of the body.
Eight different blood types
When blood is taken from one horse and given to another there is a possibility that the white blood cells and antibodies will attack the recipients blood or the white blood cells, and antibodies in the recipient can attack the red blood cells from the donor. To minimise this risk matching blood donors and recipients by blood type can be done. Humans have four major blood types and can be either negative or positive based on the rhesus factor, but horses have eight blood types and can be positive or negative on over 30 different factors. This makes getting a 100% match, a one in half a million chance. However, there are only two real problem blood types to be concerned about, Qa and Aa. So, we can cross match the donor and recipient by mixing the two bloods together and looking for a reaction before administering the blood. This being said, a blood transfusion between two horses that have never received blood transfusions previously is unlikely to result in a reaction.
An ideal blood donor will be a large (>500kg) young, healthy horse. The horse cannot have or have had a blood disease (such as equine infectious anaemia) and cannot have had a blood transfusion previously, this is because if a horse has had a blood transfusion then its immune system has produced antibodies ready to fight against other blood types, these horses won’t match. Females and especially females that have had a foal, are also more likely to carry antibodies against different blood types, that may attack the recipient of the blood.
If your horse is donating blood, then the procedure is relatively innocuous. A catheter is placed in the horse’s jugular and 4-8L of blood is collected and mixed in a prepared sterile bag. The bag contains an anti-clotting preparation and stores the blood before its use. The donating horse may or may not need to be sedated and will make a full recovery after a couple of days’ rest. Horses can donate 20-25% of their blood volume at two to four weekly intervals, however, we do try not to take this amount on a regular basis.
Blood once it is collected, can either be given as whole blood, which is usually given to horses that have lost blood through haemorrhage, or as plasma only (blood without the red blood cells). All blood products are best used fresh, but plasma can be frozen and stored for a longer period of time. Plasma also has fewer risk factors compared to whole blood, so is generally safer to administer and doesn’t require blood typing donor horses. Plasma may be administered to horses that are suffering from colic, colitis and numerous other conditions.
Because equine blood can’t be stored it is often a case of getting the blood as and when you need it. For this reason, if your horse is a blood donor you may not be required to donate for weeks or even months, but when your horse does donate, it will allow you to participate in a lifesaving treatment protocol.