The kinetics of hematopoiesis in the light horse II. The hematological response to hemorrhagic anemia.

Hemorrhagic anemia was experimentally produced in three Standardbred horses by removing approximately 63% of the red cell mass and the accompanying plasma during a three day interval. Red cell parameters were examined daily for 45 days and then weekly until termination of the experiment 250 days after production of the anemia. Leukocytes, platelets and bone marrow aspirates were examined at regular intervals for 25 days after the final phlebotomy. At 24 hours after the last bleeding, 75-selenomethionine was injected intravenously to measure the lifespan of the newly produced erythrocytes. The erythrocyte lifespan was found to be 139 days as compared to the 155 day erythrocyte lifespan for three normal standardbred horses measured previously by similar techniques. The maximum decrease in erythrocyte numbers occurred four, two and two days following the last phlebotomy to 43, 39 and 44% of the original values. The prebleeding erythrocyte levels were regained at approximately 63, 91 and 98 days respectively. During the initial 45 days post phlebotomy the maximum increase in mean cell colume was 2, 4 and 7 mj-3 respectively. During the recovery period there was erythrocyte production of 6.84, 6.99, and 6.12 x 10-9 cells/kg/day. At the same time the absolute production of hemoglobin was 44.6, 50.0, and 51.0/gm/day or on a relative basis 0.096, 0.114 and 0.113 gm/kg/day.