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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. 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. 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. 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. 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. 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.

Summary:
Prepare the donor horse for blood collection. Collect the required amount of blood. Prepare the recipient horse for the transfusion. Monitor the horse's vital signs as the transfusion is performed. Watch the horse closely following the transfusion. Feed the recipient horse a nutrient-rich diet following the transfusion.