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When a horse loses a large quantity of blood in a short amount of time, or when deficiencies in blood such as severe anemia occur, a blood transfusion may be required. Horses have approximately 40 litres of blood and can lose up to 10 litres without signs of severe shock, however, beyond a 10 litre blood loss a horse may require transfusion.
Equine blood does not store well and a stored supply of typed blood for your horse is usually unavailable. Blood for a transfusion between horses is generally taken at the time the blood is required and immediately transfused to the recipient horse. Another complication of blood transfusions in horses is that horses have eight different blood types and 30 factors for which they may be positive or negative, making locating an exact match, especially in an emergency, impossible. Horses can be tested at the time of required donation by mixing the blood of the donor horse with that of the recipient and looking for signs of clotting which would indicate incompatibility. A transfusion from an available horse, preferably one with a blood type that is less likely to cause negative side effects, can be conducted once, and generally the first blood transfusion from a horse that is not an exact match is tolerated by the recipient horse. As the situation is usually an emergency this may be the only option available. Less than 20% of blood volume is usually taken from the donor horse, who should be free from infectious disease. Some university veterinary hospital and practices keep a population of typed horses for donation. If your horse has lost a large amount of blood in a short period of time a blood transfusion performed by a veterinarian may be critical to your horse's survival.
If your horse has lost a large volume of blood or has disease causing anemia, your veterinarian will test your horse to determine their packed cell volume (PCV) which is a measure of the percentage of red blood cells capable of carrying oxygen in your horse's body. The average is 32 to 52%; a measure of 12% or less would indicate the need for a transfusion. Your veterinarian may also check hemoglobin levels which bind oxygen; if hemoglobin levels are low this would also be an indication that blood transfusion is required.
Because there are eight major blood type groups (A, C, D, K, P, Q ,T and U) and 30 possible subtypes, making for a total possible combination of 400 000, finding an exact match for your horse is impossible. Therefore, your veterinarian will use several guidelines to get a near match, which is likely to produce the most limited chance of adverse reaction.
Horses from A, C, or Q will be avoided as this type of blood is most likely to cause an antigen reaction if blood type of the recipient does not match. D, K, P and U are safer blood types to use for a first donation, even if blood types do not match. Samples of blood from the recipient and donor can be added to a test plate to look for signs of a negative reaction such as clotting or bursting cells. If this does not occur, blood is a compatible, although subtype may not be exact. In an emergency situation, time is of the essence and as close a match as possible will be utilized. Negative reaction to the first blood transfusion, even if match is not exact, does not usually occur. However, if a second transfusion is required a match will need to be located.
The donor horse will be prepared for blood collection; the hair in an area over the jugular vein will be clipped and the area cleaned. A large 10 to 14 gauge catheter will be used so red blood cells are not damaged. The needle and catheter are inserted into the vein and blood collected through tubing into a sterile container with a vacuum which will “suck” the blood into the container. The container contains a preservative to keep the blood from clotting. The reservoir is gently manipulated to prevent clotting but not damage cells. The maximum donation is 15-18 ml/kg body weight. For the average horse, this is about a 7.5 litre donation and takes 1.5 hours to collect. Blood collected should be used within a few hours as it will begin to degrade quickly.
The recipient horse is prepared for transfusion by clipping and cleaning an area over their jugular vein and inserting a 10 to 14 gauge catheter. The donation receptacle is held above the horse's head to allow it to flow with gravity into the recipient horse. Because of issues with blood typing for horses, the recipient horse will be closely monitored during this procedure for changes in vital signs that would indicate a negative reaction to the donor's blood. Blood should be introduced slowly at first until reaction can be gauged. If signs of adverse reaction occur transfusion will be stopped. Transfusion may take 1-2 hours to complete. When transfusion is complete, the catheter is either capped or withdrawn and pressure applied to stop bleeding.
Because equine blood does not store well and there are thousands of possible combinations, blood transfusion in horses is complex and success depends on the availability of a donor with a “safe” blood type available. Horses of the same breed are more likely to have similar blood types, also gelding are better donors than mares who have foaled as mares may have developed antigens in their blood to foals they were carrying. Donor horses that have previously had transfusions are not good candidates as they may have antigens developed from non-exact blood transfusions Donor horses must be free of infections diseases in order for a successful outcome to be achieved. Large horses are able to donate more blood than small ones and this also may impact the success of the transfusion if a large amount of blood is required. Because exact matches are impossible, the aim of transfusion in horses is to buy time for the horse to manufacture their own red blood cells to replace cells lost.
After a transfusion, your horse must be closely monitored for signs of a negative reaction. Also, your horse should be put on stall rest, and feed and fluid intake and output closely monitored, as organ damage from blood loss is possible. Monitoring your horse's activity, urine, and digestive processes will give an indication if this has occurred. Your horse should be given a nutritious diet with adequate vitamins and minerals such as iron, to allow them to manufacture their own red blood cells.
Many factors go into procuring an appropriate donor horse and affect the cost of blood transfusion in your horse. In addition, treatment of the trauma or condition causing hemorrhage varies widely depending on the case. The transfusion itself, if a donor horse is available and not including the cost of veterinary care to address cause, ranges from $500 to $1,000. Location of the procedure is also a factor, as on-site requirement for a veterinarian during the procurement and transfusion can require several hours and will incur increased charges for time and mileage Treatment at a veterinary hospital may be more economical if assistants can be engaged in the collection and transfusion process.
Complications in finding an exact match and the inability to store equine blood are complicating factors in equine blood transfusion.
Although initial transfusions are usually successful, repeat transfusions are risky if an appropriate donor match cannot be obtained and anaphylactic reaction may occur. If anaphylactic reaction occurs, the transfusion must be stopped immediately and the horse treated with adrenaline and steroids.
There is also a risk of infection or disease being transferred from the donor horse if the donor’s health is not verified.
As situations where blood transfusion is required are usually emergency cases, risks are usually acceptable as an alternative is not available.
Vaccinating horses will ensure a larger population of donor horses free from infection. Mares that are foaling should be monitored and assistance provided if complications occur to prevent postpartum hemorrhaging. Ensuring your horse has a safe stalling and turnout environment will prevent accidents that could result in major blood loss requiring transfusion.
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