The cellular component of blood comprising the red and white blood cells. The haematrocrit is expressed relative to blood volume and is evaluated after centrifugation of the blood (giving rise to its other name 'packed cell volume'). Normal haematocrit values of adult horses lie between 37 and 47%. Due to the horse's ability to release additional red blood cells from the spleen during maximal exertion, the horse can increase its haematocrit up to 65%.