Hair Cortisol and DHEA-S in Foals and Mares as a Retrospective Picture of Feto-Maternal Relationship under Physiological and Pathological Conditions

Simple Summary Hair hormone concentrations represent an attractive alternative for studies focusing on the prenatal period because a single measurement from hair collected at birth could provide data from a wide but datable prenatal period. Our aim is to evaluate cortisol, dehydroepiandrosterone-sulfate concentrations and their ratio in the trichological matrix of mares and foals to assess maternal and fetal hypothalamus-pituitary-adrenal axis activity in relation to the clinical condition of the neonate and the housing place at parturition. Mare's endocrine setting influences hormone concentrations detected in foal's hair, and foals classified as sick at birth have different hormone concentrations than healthy ones. On the other hand, hormone concentrations detected in the hair of mares hospitalized for attended parturitions do not reflect a different hypothalamus-pituitary-adrenal axis activity from those foaled at the breeding farm. Although the specific role of cortisol and dehydroepiandrosterone-sulfate in foals and mares under pathological conditions remains under investigation, this study opens up the use of neonate's hair as an attractive non-invasive retrospective calendar for the assessment of prenatal adrenal activity in the equine species. Equine fetal hair starts to grow at around 270 days of pregnancy, and hair collected at birth reflects hormones of the last third of pregnancy. The study aimed to evaluate cortisol (CORT) and dehydroepiandrosterone-sulfate (DHEA-S) concentrations and their ratio in the trichological matrix of foals and mares in relation to their clinical parameters; the clinical condition of the neonate (study 1); the housing place at parturition (study 2). In study 1, 107 mare-foal pairs were divided into healthy (group H; n = 56) and sick (group S; n = 51) foals, whereas in study 2, group H was divided into hospital (n = 30) and breeding farm (n = 26) parturition. Steroids from hair were measured using a solid-phase microtiter radioimmunoassay. In study 1, hair CORT concentrations measured in foals did not differ between groups and did not appear to be influenced by clinical parameters. A correlation between foal and mare hair CORT concentrations (p = 0.019; r = 0.312, group H; p = 0.006; r = 0.349, group S) and between CORT and DHEA-S concentrations in foals (p = 0.018; r = 0.282, group H; p < 0.001; r = 0.44, group S) and mares (p = 0.006; r = 0.361, group H; p = 0.027; r = 0.271, group S) exists in both groups. Increased hair DHEA-S concentrations (p = 0.033) and decreased CORT/DHEA-S ratio (p < 0.001) appear to be potential biomarkers of chronic stress in the final third of pregnancy, as well as a potential sign of resilience and allostatic load in sick foals, and deserve further attention in the evaluation of prenatal hypothalamus-pituitary-adrenal (HPA) axis activity in the equine species. In study 2, hormone concentrations in the hair of mares hospitalized for attended parturition did not differ from those that were foaled at the breeding farm. This result could be related to a too brief period of hospitalization to cause significant changes in steroid deposition in the mare's hair.

Automated summary

The study aimed to evaluate hormone concentrations in the hair of mares and foals in relation to their clinical parameters. The results showed that mare's endocrine setting influences hormone concentrations in foal's hair, and foals with different clinical conditions have different hormone concentrations. Furthermore, hormone concentrations in the hair of mares hospitalized for attended parturition did not differ from those at the breeding farm.