How to Approach Whole Blood Transfusions in Horses

Three Parts:Preparing the TransfusionCollecting and Transfusing the BloodDealing With Complications

An equine blood transfusion is an emergency procedure that provides temporary, but potentially life-saving benefits. This article discusses the preparatory steps needed for both the donor and recipient horses, the process involved in transfusing the blood and the possible risks. Just see Step 1 below to get started.

Part 1
Preparing the Transfusion

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    Give your horse a blood transfusion only in life-threatening situations. Because of the complications associated with equine blood transfusions, this procedure is best saved for life-threatening occasions when the benefits outweigh the potential risks.
    • Situations where this might arise would be severe, uncontrolled hemorrhage caused by a severed artery, or blood loss form the womb after foaling.
    • Another indication is severe anemia because of autoimmune disease, where the body has attacked its own red blood cells. In this situation, a transfusion may be appropriate to buy time while treatment kicks in, and give the bone marrow time to regenerate replacement red blood cells.
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    Have the vet check your horse's PCV. The main marker your veterinarian will use to decide whether your horse needs a blood transfusion is the horse's packed cell volume (PCV). This is a measure of the percentage of fluid blood taken up by red blood cells.
    • A healthy horse has a PCV in the range of 32-52%. The threshold at which transfusion is indicated is 12% or below.
    • At this level, the blood is unable to deliver sufficient oxygen to the tissues to maintain function and so supplementary help in the form of a transfusion is required.
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    Allow the vet to check your horse's blood hemoglobin levels. Another marker used by your veterinarian during the decision process is the horse's blood hemoglobin levels.
    • Hemoglobin binds to oxygen, so low levels imply inadequate oxygenation of the tissues. A normal level is 11-19g/dl of blood, if this falls below 8g/dl than transfusion is advisable.
    • Both PCV and hemoglobin can be measured by the blood machines that most modern vet clinics have on site, and the results made available within minutes of the test being run.
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    Though it may be difficult, try to find a donor with a matching blood type. There are 8 major equine blood groups: A, C, D, K, P, Q, U, and T. However, each of these groups is further subdivided into subtypes because of slight variations in the proteins (alloantigens) on the surface of the red blood cells.
    • The total combination of individual blood types has been calculated at somewhere over 400,000, thus finding a donor that is an exact match for the recipient is almost impossible.
    • Because of this, the aim of equine transfusion medicine is to cross match donor and recipient blood in order to eliminate the groups of blood most likely to cross react and cause a severe reaction.
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    Avoid donor horses from blood groups A, C, or Q. Blood donation from groups A, C, and Q are most likely to stimulate an antibody response if the recipient is not of those groups.
    • Horses with the blood group A, C, or Q are generally avoided as donors because their blood is highly immunogenic (over stimulates the immune system) and likely to cause a major transfusion reaction.
    • If the donor does not have a crisis with the first transfusion, if she receives a second then it a catastrophic reaction involving serious complications (as described in section three below) is guaranteed.
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    Look for a donor horse with blood type D, K, P or U. Horses from the remaining groups, i.e. D, K, P, and U are considered safe donors. It is preferable for a recipient to receive blood from as close a match of group as possible, but if a group D horses urgently needs a blood transfusion, then a donor from groups D, K, P, or U is acceptable as these groups are classed as universal donors (safe to give the first transfusion to any horse).
    • The reason why finding a horse with as close a blood type as possible is because the horse's body is programmed to accept the presence of its own blood as harmless and not mount an immune response (produce antibodies) against it.
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    Perform blood typing on a sample of the horse's blood. Blood-typing is a simple procedure that involves applying spots of the donor horse's blood to a special test plate.
    • This test plate is impregnated with antibodies to each of the different blood groups. When the sample is applied, the blood cells either clump together or burst. The one test plate where the blood does not clump together denotes the correct blood type, because it has not triggered a reaction.
    • In an ideal world both donor and recipient would be typed and as close a match as possible given (i.e., a group U horse would receive group U blood.) However, in an emergency situation this may not be possible, so only the donor horse is typed to ensure he is a universal donor (groups D, K, P, and U).

Part 2
Collecting and Transfusing the Blood

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    Prepare the donor horse for blood collection. The donor horse is confined to a stall or stock. A patch of hair is clipped over the jugular vein in the neck and the skin is disinfected with a surgical scrub such as hibiscrub or iodine.
    • A large gauge catheter (10gauge) or needle (14gauge) is required so that the red blood cells are not physically damaged as they flow through into the collection tubing and container.
    • The needle is inserted into the vein and the hub connected to blood collection tubing. This is a length of clear, flexible, sterile tubing through which the blood flows into a collecting container.
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    Collect the required amount of blood. The blood collection container contains a vacuum, so the negative pressure continues to suck the blood out of the donor horse's circulation. The bottle contains ACD preservative which stops the blood from clotting once it has been collected.
    • As the blood is collecting, gently swirl or rock the bottle to mix it with the preservative. Never shake the bottle, as this could cause the red blood cells to become burst or damaged.
    • The maximum volume of blood that can be collected from one horse is 15-18 ml/kg body weight, once a month. Thus a 500-600kg horse provides approximately 7.5 liters (2.0 US gal) of blood per month, and it takes around 1.5 hours to harvest.
    • Once obtained. a blood sample should be used within 4 hours.
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    Prepare the recipient horse for the transfusion. The recipient horse's jugular vein is prepared in the same way as for the donor horse, and a 10g catheter or 14 gauge needle inserted into the vein.
    • The giving set on the blood container is attached to the needle or catheter and the blood is elevated above the horse's head to allow gravity to assist with the delivery.
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    Monitor the horse's vital signs as the transfusion is performed. The recipient horse's heart and respiratory rate, body temperature, and the color of the mucus membranes of the mouth are recorded before the transfusion starts, and every 2 minutes thereafter for the first 10 minutes of the transfusion.
    • For the first 10 minutes the transfusion is given slowly, at a rate of 0.1ml/kg body weight. This allows the veterinarian to check for the early signs of a transfusion reaction. If a transfusion reaction is detected, the transfusion will be stopped before the recipient receives a large volume of donor blood.
    • If no signs of a reaction occur, then the flow rate is increased to 20-30ml/kg body weight per hour. Thus a transfusion involving a 500kg horse receiving 7.5 liters (2.0 US gal) of whole blood takes half an hour to complete.
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    Watch the horse closely following the transfusion. A blood transfusion buys the horse enough time to manufacture new red blood cells in the bone marrow. The transfusion provides enough increase in circulatory volume to stop damage to the major organs and take the horse out of immediate danger.
    • However, the horse will still be weak following the transfusion and a period of box rest to aid recovery is essential. This also enables the horse's food intake to be monitored, along with her water intake and urine output.
    • Closely monitoring these things is very important, because if the hemorrhage was severe enough to cause organ damage, the early warning signs are increased thirst, and increased urine production.
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    Feed the recipient horse a nutrient-rich diet following the transfusion. The recipient horse should be fed a highly nutritious, iron-rich diet following the blood transfusion, to ensure that they have all the nutrients necessary for red blood cell production.
    • These diets usually consist of a highly palatable muesli formulation that is protein dense and provides a greater density of calories than regular foods. Thus, if the horse's appetite is reduced, they still take in energy.
    • This muesli also has added B vitamins to help appetite, and is rich in antioxidants to encourage healing.

Part 3
Dealing With Complications

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    Watch out for an anaphylactic reaction during a second blood transfusion. A blood transfusion is considered a success if the donor cells survive 5 to 7 days in the recipient's circulation. This is because the huge range of equine blood types makes an exact match almost impossible.
    • The aim of the transfusion is to buy time while the recipient's bone marrow makes replacement red blood cells. For a first blood transfusion, the recipient's immune system swings into action over a relatively long period of a few days.
    • For a second transfusion, (where antibodies to the foreign blood already exist) or if an incompatible blood type is given, a much more violent, or anaphylactic reaction can happen.
    • Other potential complications include transfusing the horse with infected blood, or giving blood that contains too much anti-coagulant. The latter interferes with the natural clotting ability of the blood and could lead to hemorrhage.
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    Know what is meant by anaphylaxis. Anaphylaxis is a classic type I hypersensitivity reaction. In short, it causes the body to activate its immune system to get rid of foreign cells, but the immune system overreacts and the body goes into a state of shock and circulatory collapse.
    • If the transfusion continues, or treatment for the anaphylaxis is not given, the horse will collapse and die - sometimes as soon as 20 minutes after starting the transfusion.
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    Look for symptoms such as fever, shaking and rapid breathing. As mentioned above, an anaphylactic reaction is the sudden switching on of the recipient horse's immune system such that it attacks the donor blood cells, causing them to burst within a few minutes of administration.
    • These damaged cells release their contents, including potassium and hemoglobin, into the blood stream. Signs that this is happening include fever, shaking, rapid shallow breathing, a racing heart rate, jaundiced whites of the eyes and gums, and urine with a bright orange or strong yellow color.
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    Treat anaphylaxis with adrenaline and steroids. If the horse starts to shake, breathe quickly, and has an erratic heart rate the transfusion must be stopped and treatment for anaphylaxis must be administered immediately.
    • Treatment involves the administration of adrenaline at a rate of 1:1000, 5ml per 500kg body weight by intramuscular injection. This improves circulatory function.
    • An intravenous steroid injection should also be given to switch off the immune reaction that is destroying the cells. The dose is 0.5-1mg/kg of dexamethasone, which is equivalent to 20ml of 0.2% solution for a 500 kg horse.
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    Use an adrenaline shot to counteract anaphylaxis and reverse shock. Adrenaline is a hormone and nerve transmitter that stimulates specific receptors in blood vessels and the heart, helping to reverse shock.
    • It does this by causing a contraction of the minor blood vessels, allowing the blood volume to become concentrated in the major blood vessels. This provides a greater supply of blood to the vital organs.
    • Adrenaline also causes the heart to pump more strongly and hence push blood around the circulation more effectively. This allows oxygenated blood to reach the brain and other vital organs more quickly.


  • To decrease the chance of the donor accidentally infecting the recipient it is advised that donor animals are up to date with rhinopneumonitis vaccine, tetanus toxoid, Eastern and Western encephalitis vaccine, botulism toxoid, rabies toxoid, and are annually confirmed negative for equine infectious anemia (EIA), and equine viral arteritis (EVA).

Sources and Citations

  • Survival of 59 Fe-labelled erythrocytes in cross-transfused equine blood. Kallfelz, Schultz. Am J Vet Research. 1978: 39, 617 – 630
  • Blood banking and transfusion medicine. Ettinger, Feldman. Textbook of veterinary internal medicine. WB Saunders. 4th edition

Article Info

Categories: Horse Care