Research articleChanges in blood pressure, heart rate, and blood profile in mares during the last 3 months of gestation and the peripartum period

In this study, peripartum changes in complete blood count, plasma electrolyte concentrations, blood pressure, heart rate, and heart rate variability (HRV) were determined in pregnant Warmblood mares (n = 10). Blood was collected from Days 245 to 330 of gestation (phase A), 2Days 3 to 1 before foaling (phase B), repeatedly within 12 hours after foaling (phase C), and on Days 1 to 3 postpartum (phase D). On the same days as blood collection, blood pressure and cardiac beat-to-beat intervals were measured and time domain HRV variables were calculated. Blood pressure decreased during the past 3 months of gestation, reached a nadir at foaling and increased rapidly thereafter (P < 0.001). Heart rate increased in phase A, reached a maximum in phase B, and decreased directly after foaling (P < 0.001) while HRV increased transiently after foaling (P < 0.001). The number of polymorphonuclear granulocytes was higher during phases B, C, and D than that during phase A (P < 0.001) and total leukocyte numbers peaked in phase C (P < 0.001). Erythrocyte counts and hematocrit increased immediately after foaling with a rapid decrease thereafter (P < 0.001), while plasma total protein was highest 1 hour after foaling (P < 0.001). Sodium and chloride concentrations increased from phases A to C and decreased in phase D (P < 0.001). Calcium concentrations were lowest immediately after foaling. In conclusion, changes in cardiovascular function and a transient hemoconcentration occur in peripartum mares. These changes may favor adequate uterine perfusion.