The effect of physical exercise on the daily rhythm of platelet aggregation and body temperature in horses.

The goal of this study was to investigate the influence of physical activity on the daily rhythm of platelet aggregation and body temperature in horses. Blood samples from 12 Thoroughbred horses, six sedentary animals and six athletes (studied both before and after a period of inactivity) were collected at 4h intervals for 48h via an intravenous cannula inserted into the jugular vein. Body temperature was recorded every 4h for 48h with a rectal probe. Platelet aggregation was measured with an aggregometer. Collagen was used to test the aggregation of the plasma samples. Statistical analysis of the data was performed by one-way repeated-measures analysis of variance (ANOVA) and by single cosinor method. Cosinor analysis identified the periodic parameters and their acrophases (expressed in hours) during the 2 days of monitoring. On each single day, there was a highly significant effect of time in all the horses, with P values <0.05. Temperature rhythms were unaffected by exercise. Platelet aggregation in exercising horses differed from the sedentary horses, and this difference disappeared after a 2-week period of rest. The results could be interpreted as indicating that physical exercise has an influence on the daily rhythm of platelet aggregation in horses.