Christina Nagel

Cortisol and progestin release, heart rate and heart rate variability in the pregnant and postpartum mare, fetus and newborn foal

The mechanisms leading to parturition in the horse in many aspects differ from those in other species. Pregnancy is maintained not by progesterone but by 5α-pregnanes and the progestin precursor pregnenolone originates from the fetus. As parturition approaches, the fetal adrenal switches from pregnenolone to cortisol synthesis but it is not known whether cortisol crosses the placenta. We hypothesized that in parallel to fetal cortisol release, cortisol in the maternal circulation increases before foaling and this increase can be determined in both saliva and plasma. In addition, maternal, fetal and neonatal heart rate and heart rate variability were measured. In 25 pregnant mares, saliva for cortisol analysis was collected 4 times daily from 15 days before to 5 days after foaling. In 13 mares, in addition, fetomaternal electrocardiogram (ECG) recordings were made and blood samples for progestin and cortisol analysis were collected once daily. Heart rate (HR) was recorded until 5 days after foaling. The heart rate variability (HRV) variables standard deviation of the beat-to-beat (RR) interval (SDRR) and root mean square of successive RR differences (RMSSD) were calculated. From Days 15 to 4 before parturition, progestin concentration increased (peak 267 ± 42 ng/mL) and decreased thereafter (P < 0.05, day of foaling 113 ± 18 ng/mL). A prepartum increase in maternal cortisol concentrations was evident in blood (P < 0.05) and saliva (P < 0.05) and paralleled the decrease in progestin concentrations. In mares, HR remained constant during the last days of pregnancy but decreased within one day after parturition (P < 0.05) while maternal HRV did not change. In the fetus and neonate, HR increased from before to after birth (P < 0.05) indicating increasing demands on the cardiovascular system with adaptation to extrauterine life.

Determination of heart rate and heart rate variability in the equine fetus by fetomaternal electrocardiography

Heart rate is an important parameter of fetal well-being. We have analyzed fetal heart rate (HR) and heart rate variability (HRV) by fetomaternal electrocardiography (ECG) in the horse (Equus caballus) from midpregnancy to foaling. It was the aim of the study to detect changes in the regulation of fetal cardiac activity over time and to establish normal values in undisturbed pregnancies. A total of 22 mares were available for the study. Fetomaternal electrocardiography was a reliable technique to detect cardiac signals in fetuses between Day 173 of gestation and foaling. Fetal HR decreased from 115+/-4 beats/min (Days 170 to 240 of gestation) to 83+/-3 beats/min (Day 320) to 79+/-1 beats/min (1 d before foaling; P<0.001). Mean beat to beat (RR) interval and standard deviation of the RR interval (SDRR) increased (P<0.001). Gestational age thus affects RR interval and HR in the equine fetus. From Days 270 to 340 of gestation, SDRR increased from 11.4+/-1.3 msec on Day 270 to 27.8+/-3.6 msec on Day 340 (P<0.05), and the root mean square of successive RR differences (RMSSD) tended to increase (P=0.07), indicating maturation of the fetal autonomous nervous system. For the last 10 d before foaling, fetal HR and HRV remained constant and did not allow predicting the onset of parturition in the horse. Only during the last 30min before the foal was born, in 4 of 5 fetuses, HR decreased and RR interval increased. Accelerations and decelerations in HR were detectable at all times, but neither their number nor duration changed over time.

Parturition in horses is dominated by parasympathetic activity of the autonomous nervous system.

External and internal stressors prolong parturition in different species. At parturition, sympathoadrenal activation should be avoided because an increased sympathetic tone may cause uterine atonia via β2-receptors. We hypothesized that at physiological parturition, horses are under parasympathetic dominance, and stress-response mechanisms are not activated during delivery of the foal. To evaluate stress responses, heart rate, heart rate variability, catecholamines, and cortisol were analyzed in mares (n = 17) throughout foaling. Heart rate decreased from 2 hours before (51 ± 1 beats/minute) to 2 hours after delivery (41 ± 2 beats/minute; P < 0.05). Heart rate variability variables, standard deviation of the beat-to-beat interval, and root mean square of successive beat-to-beat differences, changed over time (P < 0.05) with the highest values within 15 minutes after delivery. The number of mares with atrioventricular blocks and the number of atrioventricular blocks per mare increased over time (P < 0.01) and were significantly elevated from 15 minutes before to 45 minutes after birth of the foal. Salivary cortisol concentrations increased to a maximum at 30 minutes after delivery (25.0 ± 3.4 ng/mL; P < 0.01). Plasma epinephrine and norepinephrine concentrations showed significant fluctuations from rupture of the allantochorion to expulsion of the fetal membranes (P < 0.01) but were not markedly elevated at any time. In conclusion, mares give birth under high parasympathetic tone. Cortisol release during and after foaling is most likely part of the endocrine pathways regulating parturition and not a labor-associated stress response.

Heart rate and heart rate variability in the pregnant mare and its foetus.

Abortion and preterm birth of foals are major reasons for reproductive losses in the horse. Risk pregnancies require close supervision so that adequate treatment can be initiated in time. The aim of this study was to determine normal values in heart rate (HR) and heart rate variability (HRV) of the pregnant mare compared to her foetus and to detect physiological changes during ongoing gestation. In mares, the RR interval decreased from 1480±29 ms on day 270 of pregnancy to 1190±58 ms on day 330 of pregnancy (p<0.05). In contrast, foetal RR interval increased during the same time period from 611±23 ms on day 270 of gestation to 756±25 ms on day 330 of gestation (p<0.05). Concomitantly, maternal HR increased and foetal HR decreased. No further changes in RR interval occurred during the last 10 days before foaling, neither in the mare nor the foetus. In the last hours preceding parturition, maternal RR interval was lower than at all times earlier in pregnancy (average of 1037±13 ms) but did not change during this time. Maternal HRV did not change during gestation. Marked changes in HRV occurred only during the last minutes of foaling. Then, all HRV variables increased significantly (standard deviation of beat-to-beat interval: p=0.01, root mean square of successive beat-to-beat differences: p<0.01). The cardiovascular system of pregnant mares adapted to the demands of ongoing pregnancy with an increase in HR. We have no evidence that in healthy mares, pregnancy is a major stressor.

Heart rate and heart rate variability in pregnant warmblood and Shetland mares as well as their fetuses

Heart rate (HR) is an important parameter of fetal well-being. In horses, HR and heart rate variability (HRV) can be determined by fetomaternal electrocardiography (ECG) from mid-pregnancy to foaling. Normal values for physiological parameters in larger breeds are often used as reference values in ponies. However, HR increases with decreasing size of the animal and in ponies is higher than in warmblood horses. It is not known if fetal HR is affected by breed and if values obtained in larger breeds can be used to assess Shetland fetuses. We have determined fetomaternal beat-to-beat (RR) interval (inversely correlated to HR) and HRV in warmblood (n=6) and Shetland pregnancies (n=7) at days 280 and 300 of gestation by ECG. Maternal RR interval was lower in pony than in warmblood mares (day 280: Shetland: 958±110, warmblood: 1489±126ms, p<0.01) The SDRR (standard deviation of RR interval) and the RMSSD (root mean square of successive RR differences) did not differ between breeds at any time. Also RR interval as well as HRV did not differ between warmblood and pony fetuses (RR interval day 280: Shetland: 606±39, warmblood: 589±38ms). In conclusion, although maternal RR interval is clearly higher in Shetland than in warmblood mares, fetal RR interval in the two breeds is on the same level.

The PGF2α agonists luprostiol and d-cloprostenol reliably induce luteolysis in luteal phase mares without evoking clinical side effects or a stress response

In the present study we have evaluated a possible stress reaction in response to two different PGF2α analogs-luprostiol and D-cloprostenol--and their effects on estrous cycle characteristics. In a cross-over-design eight mares received in alternating order either luprostiol (Treatment LUP; 3.75 mg im), D-cloprostenol (Treatment CLO; 22.5μg im) or saline (Treatment CON; NaCl 0.9% 0.5ml im) on day 8 after ovulation. Injection of either LUP or CLO, but not of CON resulted in a significant decline of progesterone concentration in plasma to baseline concentrations within two days (time: p<0.001, treatment: p<0.01, time × treatment: p<0.05). The treatment to ovulation interval was significantly shorter in LUP and CLO than in CON cycles (LUP: 9.4 ± 0.4 d; CLO: 9.4 ± 1.3 d; CON: 16.1 ± 0.8 d; p<0.001). Injection of either LUP or CLO, but not of CON significantly increased salivary cortisol concentration (immediately before injection: CON 1.3 ± 0.2, LUP 1.4 ± 0.3, CLO 1.4 ± 0.3 ng/ml; 60 min after injection: CON 1.0 ± 0.3, LUP 8.0 ± 1.4, CLO 4.2 ± 0.7 ng/ml; time: p<0.01, treatment: p<0.001, time × treatment: p<0.001). Heart rate decreased over time (p<0.05) independent of treatment and no changes in heart rate variability were detected. Injection of the PGF2α analogs CLO and LUP reliably induced luteolysis and apart from a transient increase in salivary cortisol concentration no signs of a physiological stress response or apparent side effects occurred.

Distribution of ventilation in pregnant Shetland ponies measured by Electrical Impedance Tomography.

The regional distribution of ventilation in conscious standing pregnant Shetland pony mares was investigated by Electrical Impedance Tomography (EIT). Six ponies were repeatedly examined a minimum of four weeks prior to (antepartum, AP) until three weeks after parturition (postpartum, PP). From the cross-sectional ventilation image the ventral to dorsal (V/D), left to right (L/R) ventilation distribution ratio and the relative ventilation in four horizontal regions of interest (ROI) placed symmetrically in the chest was analyzed. Antepartum V/D was 0.74 ± 0.09 on day -28 ± 3 (AP28) and decreased to 0.68 ± 0.10 on day -3 ± 2 (AP3). Postpartum V/D increased significantly (p<0.05) to 0.96 ± 0.08 on day 7 ± 2 (PP7). The L/R ventilation distribution remains unaffected. Ventilation in the most ventral ROI was significantly lower on days AP28 and AP3 compared to PP7. These results suggest that in Shetland ponies late pregnancy compromises the ventilation in ventral (dependent) lung regions. We demonstrated the feasibility of a repeated EIT measurement in standing conscious ponies.

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 salivary cortisol concentrations in foals at birth.

Heart rate (HR), HR variability (HRV) and salivary cortisol concentrations were determined in foals (n = 13) during the perinatal phase and until 5 months of age. In the fetus, HR decreased from 77 ± 3 beats/min at 120 min before birth to 60 ± 1 beats/min at 5 min before birth (P <0.01). Within 30 min of birth, HR increased to 160 ± 9 beats/min (P <0.01). Salivary cortisol concentrations immediately after birth were 11.9 ± 3.6 ng/mL and within 2 h increased to a maximum of 52.5 ± 12.3 ng/mL (P <0.01). In conclusion, increases in HR and salivary cortisol concentrations in foals are not induced during parturition, but occur immediately after birth.

Clinical parameters, intestinal function, and IGF1 concentrations in colostrum-deprived and colostrum-fed newborn pony foals

Colostrum (COL) contains cytokines and growth factors that may enhance intestinal development in neonates. The hypothesis of this study was that besides providing immunoglobulins, COL is important for intestinal function and meconium release in foals. Newborn foals were either fed COL (n = 5) or an equal amount of milk replacer (MR, n = 7) during the first 24 hours of life. To ensure passive immunity, all foals received 1 L plasma. Postnatal development, meconium release, intestinal motility, white blood cell count, insulin-like growth factor 1, and intestinal absorptive function (xylose absorption test) were evaluated. Clinical findings and meconium release were not affected by feeding of COL or MR. Ultrasonography revealed a slightly larger jejunum and stomach in group COL versus MR (P < 0.05). The percentage of polymorphonuclear leucocytes was higher in foals of group MR versus group COL (P < 0.05) and the percentage of lymphocytes was lower in MR compared with COL foals (P < 0.05). Plasma insulin-like growth factor 1 concentration increased during the first 14 days after birth in both groups. A xylose absorption test on Day 5 revealed similar increases in plasma xylose concentrations after oral intake. In conclusion, feeding of COL versus MR was without effect on meconium release and intestinal absorptive function. Differences between foals fed COL and MR with regard to intestinal function are apparently without clinical relevance. In foals that have not received maternal COL, there is no major risk of intestinal problems if they are fed MR and provided with immunoglobulins by transfusion of plasma.