Cardiovascular, haematological and biochemical responses after large volume blood collection in horses

To determine whether removal of 20 mL/kg of blood (approximately 25% of blood volume) resulted in adverse physiological effects in donor horses, we removed this volume of blood from five horses and selected cardiovascular, haematological and biochemical variables measured during collection and for 31 days thereafter. We found that alteration in most variables occurred, although the changes in values usually remained within published reference ranges. Also, recovery of these alterations to pre-collection values was rapid, occurring within 24--48 h in most instances. We concluded that volumes of blood less than or equal to 20 mL/kg when collected appropriately from healthy donor horses result in no adverse acute or chronic physiological changes. These results suggest that horses undergo adequate physiological compensation when approximately 25% of blood volume is removed for the purposes of blood donation or production of plasma.