Neonatal histopathological findings enabling further understanding of the pathophysiological mechanisms of pregnancy failure in the common bottlenose dolphin (Tursiops truncatus)

Reproductive success is a critical component of the care of bottlenose dolphins (Tursiops truncatus) in managed care facilities and is vital in sustaining free-ranging dolphin populations. Despite well-established breeding programs with high reproductive success rates, pregnancy failures still occur in managed care just as they do in free ranging dolphin populations. Retrospective analysis from 1990-2019 enabled histopathology to be performed on neonatal tissue from 29 failed bottlenose dolphin pregnancy cases. Timing of the neonatal loss varied with three failures occurring during the 2nd trimester, 13 losses occurred in the 3rd trimester, seven neonates did not survive > 24 hours and six neonates did not survive > 30 days. These 29 cases were examined for signs of lung atelectasis, fetal distress, fetal pneumonia, and where available the placenta was also examined for signs of inflammation or pathological lesions. Fetal distress was defined as an increased number of amniotic squamous cells, with or without meconium, within the fetal bronchioles and alveoli. It was subjectively graded as mild, moderate or severe. Possible causes include: normally occurring birthing complications, infections that cause placental necrosis, fetal hypoxia secondary to placental abnormalities such as an umbilical cord torsion, decreased oxygen carrying capacity of the blood due to anemia or decreased food intake, maternal hypoxia, and maternal shock. This study aims to further elucidate the pathophysiological mechanisms of pregnancy failure in the bottlenose dolphin.