Nictemeral profile of platelet aggregation and clotting parameters in horses during training

The daily rhythm of platelet aggregation and clotting parameters during training were investigated in six Thoroughbred horses. Blood samples were collected every 4 h for 48 h. Platelet aggregation was measured with an aggregometer and subsequently according to the trends recorded, the percentage of aggregation was calculated. Prothrombin time (PT), activated partial thromboplastin time, thrombin time, and fibrinogen concentration were assessed by means of a coagulometer. A one-way repeated-measures analysis of variance was used to determine significant differences (P<0.05) and the single cosinor method was applied. On each single day, a significant effect of time on the percentage of aggregation and PT was observed. A cosinor analysis identified the nictemeral rhythm of percentage of aggregation and PT that showed a nocturnal acrophases on both days 1 and 2. We can assert that physical exercise could be an event regulating the daily rhythms of platelet aggregation and clotting parameters in the horse.