Effects of placental pathology on maternal plasma progestagen and mammary secretion calcium concentrations and on neonatal adrenocortical function in the horse.

This research investigates how placental pathology in horses affects concentrations of certain hormones and minerals in the dam, and the impact on newborn foal’s adrenocortical function and behaviour. It found that abnormal pregnancy, marked by precocious signs of parturition, could be diagnosed early through increased progestagens in the dam’s blood and that foals born from such pregnancies are often physiologically immature while having normal or intermediate adrenocortical function.

Overview of the Research

• The study was conducted between 1985 and 1990, with 25 Thoroughbred mares identified as having abnormal pregnancies due to early signs of impending parturition. Seven pony mares were used to establish a model of placental pathology by inducing placental separation.
• Throughout their pregnancies, these mares were monitored for plasma progestagen and mammary calcium secretions. After giving birth, their placentas were examined for pathologies and the foals were assessed for adrenocortical function and behaviour.
• The control group comprised 35 Thoroughbred mares and 39 pony mares, all believed to have had normal pregnancies.

Placental Pathology and Maternal Blood Concentrations

• The research found that out of the 25 mares with abnormal pregnancies, 16 had prematurely increased plasma progestagen concentrations, 17 exhibited increased mammary calcium concentrations, and 24 had an abnormal placenta detected post-partum.
• After the researchers induced placental separation in the Pony mares, they found that 4 of the 7 mares showed increased maternal plasma progestagen levels within 4-11 days, and 1 mare after 42 days.
• Three of these mares showed signs of placental pathology, and one of them aborted at 287 days gestation. Among these mares, two of the remaining mares that then did not show an increase in progestagens aborted at 240 days and 271 days.

Effects on Foal’s Adrenocortical Function and Behaviour

• From the 25 mares, 18 live foals resulted, out of which 11 appeared abnormal based on their behaviour.
• When adrenocortical function was evaluated in 13 of the foals, 4 had normal function, 3 exhibited hypofunction, and the remaining 6 were categorised as intermediate.
• Plasma progestagens were examined in 13 foals, with 7 showing normal concentrations and 6 having abnormal levels.

Conclusion

• The study concluded that placental dysfunction could be diagnosed early, before 308 days of gestation, through increases in plasma progestagen in the dam.
• Foals born in these conditions may be physiologically immature but have normal or intermediate adrenocortical function, regardless of their gestational age.
• The findings were different for foals born prematurely without maternal plasma progestagen or mammary secretion calcium increments. The study, therefore, highlights the importance of monitoring maternal plasma progestagen and mammary calcium levels in identifying and managing at-risk pregnancies in horses.