Behaviour of mean erythrocyte volume during submaximal treadmill exercise in the horse

The aim of this work was to study the role of spleen contraction in the mod ification of circulating erythrocyte mean volume during treadmill exercise in the horse. Red blood cells count (RBC), haematocrit (Hct), haemoglobin ( Hgb), mean cellular volume (MCV), mean cellular haemoglobin (MCH), mean cel lular haemoglobin concentration (MCHC) and red cell distribution width (RDW ) were evaluated in five Haflinger mares performing a submaximal incrementa l test on the treadmill. Blood was collected every minute during the trial without stopping the treadmill. Significant changes of all measured paramet ers, except for MCH, have been observed. Hct values increased significantly from the 2nd minute from the start of the test. MCV and MCHC values were s ignificantly different from their basal values from the 6th minute of exerc ise, with MCV being increased and MCHC decreased, suggesting cellular swell ing. Hct modifications during brief submaximal exercise have been shown to be mainly and directly related to mobilization of the pool of red blood cel ls stored in the spleen. However, the evidence in this study of different t imes of onset of changes between Her and erythrocyte indices (MCV and MCHC) suggests that exercise-induced alterations in red cell indices are not rel ated to spleen emptying.