Nycthemeral change of some haematological parameters in horses

Many physiological processes of domestic animals exhibit daily rhythmicity. The goal of the present study was to investigate, in horses, the existence of the daily rhythms of some haematological parameters: red blood cells (RBC), white blood cells (WBC), haemoglobin (Hb), haematocrit (Hct), mean corpuscular volume (MCV), mean corpuscular haemoglobin (MCH), mean corpuscular haemoglobin concentration (MCHC) and platelets (PLT). Blood samples from 6 Thoroughbred mares were collected at 4-hour intervals for 48 hours (starting at 08:00 hours on day 1 and finishing at 04:00 on day 2) via an intravenous cannula inserted into the jugular vein. ANOVA showed a highly significant effect of time on haemoglobin and on haematocrit, in all the horses, on either day, with p values < 0.05. Cosinor analysis identified the periodic parameters and their acrophases (expressed in hours) during the 2 days of monitoring. RBC, Hb, Hct and MCV showed nycthemeral variations included between 17.44 and 22.28, which could suggest the hypothetical influence of various exogenous factors.