Role of decreased plasma volume in hematocrit alterations during incremental treadmill exercise in horses.

This study investigated the role of decreasing plasma volume in the changes in hematocrit levels seen during incremental exercise in horses, both with and without a spleen.

Explanation of Research Paper

The researchers performed an exercise test on two groups of mares: those with their spleen intact (IN) and those that had been splenectomized (SP). The goal was to assess how decreases in plasma volume (PV), the liquid component of blood, might influence hematocrit (Hct) changes that are typically observed with exercise. Hematocrit corresponds to the proportion of red blood cells in the total blood volume.

• The exercise test involved having the horses run on a 6-degree inclined treadmill. The initial speed was set at 4 m/s and was incrementally increased every minute until the horse’s heart rate plateaued.
• Blood samples were collected at rest and at the end of each incremental increase in speed: 4, 5, 6, and 7 m/s.
• The resting PV was found to be greater in the IN group when compared to the SP group ((28.6 +/- 0.5 liters) compared with (22.7 +/- 2.2 liters))
• Exercise was found to significantly increase the Hct levels in both groups, however, the increases were significantly greater (P < 0.05) at all exercise intensities in IN compared with SP horses.
• The Hct increased quickly during the first treadmill speed increment (4 m/s) in IN horses. However, Hct increases slowed down for the 5, 6, and 7 m/s increments, paralleling the changes seen in the SP horses.
• The corrected Hct values were utilized to estimate the relative change in PV. It was noticed that exercise resulted in a significant decrease in PV in both groups. However, no significant differences (P > 0.05) existed between the IN and SP horses’ decreases in PV at the two highest speed steps of the exercise test (6 and 7 m/s).

In conclusion, this research gave some insight into the mechanism of hematocrit alterations during exercise in horses. The results evidenced that exercise-induced changes in plasma volume affect the hematocrit values in exercising horses, whether or not they have a spleen.