Differences in Endocrine and Cardiac Changes in Mares and Her Fetus before, during, and after Parturition in Horses of Different Size.
Authors: Nagel Christina, Melchert Maria, Aurich Christine, Aurich Jörg
Journal: Animals : an open access journal from MDPI
Summary
# Editorial Summary Monitoring mares and foals during late pregnancy and parturition relies heavily on endocrine markers and heart rate patterns, yet little was known about how these parameters vary across different horse breeds and sizes. Nagel and colleagues tracked 23 pregnant mares—six Shetlands, eight Haflingers, and nine Warmbloods—measuring foal and placental weights alongside maternal and fetal plasma progestin, cortisol, heart rate, and heart rate variability (HRV) from late gestation through delivery. Whilst foal weight consistently represented approximately 10% of mare weight regardless of breed, full-size mares showed significantly elevated progestin and cortisol concentrations, the highest relative placental weights, and the most pronounced cardiac changes during parturition, including regular atrioventricular blocks that occurred rarely in smaller breeds. Fetal heart rate declined more steeply in larger foals approaching birth, yet fetal HRV increased markedly immediately after birth in all groups, with the greatest response in Warmbloods. These breed-specific differences in cardiovascular responses suggest that standard peripartum monitoring thresholds may need adjustment based on horse size, and that larger breeds may experience greater physiological stress during labour—findings with important implications for risk assessment and intervention protocols during high-risk deliveries.
Read the full abstract on PubMed
Practical Takeaways
- •Monitor cardiac arrhythmias (atrio-ventricular blocks) more closely in full-size mares during parturition, as they occur regularly in this population but rarely in smaller breeds
- •Expect more pronounced cardiovascular and heart rate variability changes in full-size horses compared to small and medium-sized breeds during labour
- •Use foal weight (approximately 10% of mare weight) as a breed-independent benchmark, but account for breed-specific placental and endocrine variation when assessing fetomaternal wellbeing
Key Findings
- •Foal weight consistently approximated 10% of mare weight across all three breed sizes, but relative placenta weight was highest in full-size mares (p < 0.05)
- •Progestin concentration decreased towards parturition (p < 0.001) while cortisol concentration increased (p < 0.01), with highest baseline levels in full-size mares
- •Maternal heart rate increased before foaling with most pronounced increase in small mares (p < 0.001); atrio-ventricular blocks regularly occurred in full-size mares but only occasionally in smaller breeds
- •Fetal heart rate decreased towards birth (p < 0.001) with most pronounced decrease in full-size horses (p < 0.01); fetal HRV increased upon birth (p < 0.001)