Oxytocin treatment does not change cardiovascular parameters, hematology and plasma electrolytes in parturient horse mares.

In mares, foaling is associated with changes in hematology, plasma electrolytes, blood pressure and heart rate and it has been hypothesized that these are induced by oxytocin. To test this hypothesis, mares (n = 8-14/group) were treated with oxytocin (OT; 20 I.U.) or saline (CON) at 1 h (test A) and 12 h after foaling (test B) and during first postpartum diestrus (test C). Heart rate, heart rate variability (HRV), atrioventricular blocks, salivary cortisol concentration, blood pressure, plasma electrolytes and blood count were determined. Heart rate decreased from test A to C (P < 0.001) but at no time differed between groups. The HRV, blood pressure and occurrence of atrioventricular blocks did not change in response to oxytocin. Cortisol concentration decreased from test A to C (P < 0.001). Oxytocin induced a cortisol release in test B (time x treatment P < 0.001, time x test P < 0.001). Plasma sodium and chloride concentrations decreased from test A to C (P < 0.001) but did not differ between groups. In test A, potassium concentration increased in CON but not OT mares (time P < 0.01, time x test P < 0.01, time x treatment P < 0.05). Polymorphnuclear cell (PMN) numbers in blood decreased from test A to C (P < 0.001) while lymphocytes increased (P < 0.05). At no time PMN and lymphocytes differed between groups. Oxytocin treatment had no effect on skin temperature. In conclusion, except for a limited effect on cortisol release, oxytocin was without effect and the hypothesis of oxytocin-induced alterations in cardiac parameters, plasma electrolytes and hematology of foaling mares was not verified.

Changes 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.

Stress response and cardiac activity of term and preterm calves in the perinatal period.

This study tested the hypothesis of gestational age affecting fetal cardiac activity and the stress response at birth. Heart rate (HR), heart rate variability variables, SD of the beat-to-beat interval and root mean square of successive beat-to-beat differences, and postnatal salivary cortisol concentration were studied in calves born at term (Term, n = 7, gestation length 286.3 ± 2.1 days) or after induction of parturition (Preterm, n = 7, gestation length 279.6 ± 0.2 days). Observation periods covered the last month of gestation (phase A), the last hours before birth including the first stage of labor (phase B), and the neonatal period (phase C). Fetal HR decreased in phase A (P < 0.001) and did not differ between groups. During phase B, HR increased (P < 0.05) and was higher in Preterm than in Term calves in phases B (P < 0.05) and C (P < 0.01). In Term calves, heart rate variability increased from Day 6 until birth (P < 0.05). At birth, SD of the beat-to-beat interval was higher in Term than in Preterm calves (P < 0.01). On Day 1 after birth (phase C), HR accelerations were more frequent in Term than Preterm calves (P < 0.01), whereas decelerations were more frequent in Preterm calves (P < 0.05). Cortisol concentration increased postnatally (P < 0.001) and was correlated with gestation length (r ≥ 0.68, P < 0.01). Because of a certain degree of immaturity, the ability to cope with the stress of birth may be impaired in calves born 1 week before term.

Sympathoadrenal balance and physiological stress response in cattle at spontaneous and PGF2α-induced calving.

Increased cortisol release in parturient cows may either represent a stress response or is part of the endocrine changes that initiate calving. Acute stress elicits an increase in heart rate and decrease in heart rate variability (HRV). Therefore, we analyzed cortisol concentration, heart rate and HRV variables standard deviation of beat-to-beat interval (SDRR) and root mean square of successive beat-to-beat intervals (RMSSD) in dairy cows allowed to calve spontaneously (SPON, n = 6) or with PGF2α-induced preterm parturition (PG, n = 6). We hypothesized that calving is a stressor, but induced parturition is less stressful than term calving. Saliva collection for cortisol analysis and electrocardiogram recordings for heart rate and HRV analysis were performed from 32 hours before to 18.3 ± 0.7 hours after delivery. Cortisol concentration increased in SPON and PG cows, peaked 15 minutes after delivery (P < 0.001) but was higher in SPON versus PG cows (P < 0.001) during and within 2 hours after calving. Heart rate peaked during the expulsive phase of labor and was higher in SPON than in PG cows (time × group P < 0.01). The standard deviation of beat-to-beat interval and RMSSD peaked at the end of the expulsive phase of labor (P < 0.001), indicating high vagal activity. Standard deviation of beat-to-beat interval (P < 0.01) and RMSSD (P < 0.05) were higher in SPON versus PG cows. Based on physiological stress parameters, calving is perceived as stressful but expulsion of the calf is associated with a transiently increased vagal tone which may enhance uterine contractility.

Heart rate and heart rate variability in pregnant dairy cows and their fetuses determined by fetomaternal electrocardiography.

In this study, fetomaternal electrocardiograms were recorded once weekly in cattle during the last 14 weeks of gestation. From the recorded beat-to-beat (RR) intervals, heart rate and heart rate variability (HRV) variables standard deviation of the RR interval (SDRR) and root mean square of successive RR differences (RMSSD) were calculated. To differentiate between effects of lactation and gestation, pregnant lactating (PL) cows (n = 7) and pregnant nonlactating (PNL) heifers (n = 8) were included. We hypothesized that lactation is associated with stress detectable by HRV analysis. We also followed the hypothesis that heart rate and HRV are influenced by growth and maturation of the fetus toward term. Maternal heart rate changed over time in both groups, and in PL cows, it decreased with drying-off. During the last 5 weeks of gestation, maternal heart rate increased in both groups but was lower in PL cows than in PNL heifers. Maternal HRV did not change over time, but SDRR was significantly higher in PL cows than in PNL heifers, and significant interactions of group × time existed. On the basis of HRV, undisturbed pregnancies are thus no stressor for the dam in cattle. Fetal heart rate decreased from week 14 to week 1 before birth with no difference between groups. Gestational age thus determines heart rate in the bovine fetus. The HRV variables SDRR and RMSSD increased toward the end of gestation in fetuses carried by cows but not in those carried by heifers. The increase in HRV indicates maturation of fetal cardiac regulation which may be overrun by high sympathoadrenal activity in fetuses carried by heifers as suggested by their low HRV.