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Blood Loss in Horses

Equine veterinarians are always getting calls about horses with cuts. Often the owner is very concerned over the amount of blood that may have been lost. It takes very little blood on the ground to look like a bucket’s worth. Usually by the time I arrive, the horse that the owner thought was bleeding to death is quietly eating, and the bleeding has stopped on its own.

The word hemostasis means stopping blood flow. Horses have an unusually good hemostatic system and even large diameter blood vessels that have been sliced will retract back into tissue and seal themselves off. Another hemostatic feature in horses is the huge reserve of red blood cells in the spleen. Within seconds of excitement from any source, adrenalin is released. The adrenalin causes the spleen to contract, sending out pints of red cell rich blood. Horses also form good blood clots which further slows the hemorrhage.

In a horse losing quantities of blood other changes are occurring to maintain blood pressure. Fluid is pulled from the spaces between the cells of the body and is shifted into the blood vessels. Arteries supplying non essential areas constrict. This keeps most of the blood going to vitally important structures like the brain and the heart. That shift results in a lower body temperature and cold skin. The heart rate increases to pump around the now decreased volume of blood. However, if enough blood has been lost, the emergency measures will start to fail, and the animal will go into shock.

There is a rough rule to determine how much blood a horse has. Depending on the breed you can estimate that 6-10% of the body weight is blood. (Arabians and Thoroughbreds would be the highest, draft horses the lowest). A 1000 lb. Thoroughbred would have about 100 pounds or roughly 100 pints (50 quarts) of blood. In my research I found that a horse can lose up to 30% of its blood (in this case 15 quarts! ) and still live. In over 30 years of experience I have never seen a horse bleed to death from a laceration.

If your horse has been cut and is bleeding profusely, don’t move him. Check his temperature, pulse and respiration. Roll back his lip and check for extreme paleness. Call us. Be ready to describe exactly where the cut is and how deep. Estimate unemotionally how much blood is on the ground. Now with a clean piece of cloth apply firm steady pressure directly over the wound. Maintain that pressure for at least five minutes. Remove the pressure slowly. If the bleeding continues, reapply the pressure and double the time. Don’t worry about scarring. Most sutured lacerations in horses do not leave a scar. Above all, don’t panic. The blood system has plenty of built in reserves, or as the old horsemen used to say, “It’s a long way from his heart.”

 

-David A. Jefferson, DVM

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