From Pre-Foaling to Late Pregnancy: Cortisol, DHEA(S), Progesterone, 17-β-Estradiol, and Allopregnanolone Hair Concentration Profiles in Standardbred Mares

Pregnancy and parturition represent two important physiologic phases in female mammals, in which metabolic, behavioral, and endocrinologic changes should occur in perfect timing and interaction, leading to a normal course of gestation and the occurrence of parturition at term, allowing the birth of mature and viable offspring. The present study aimed to describe the hormonal changes recorded in the hair occurring in mares from pre-foaling to late pregnancy. The hair cortisol (C) concentrations did not show any significant variations throughout the study, while dehydroepiandrosterone (sulfate) (DHEA(S)) hair concentrations showed an increase from ST-1 to ST4 (p < 0.01) followed by a significant decrease at ST6 (p < 0.01). From ST7 to ST8, hair DHEA(S) concentrations increased significantly (p < 0.01). In ST7 the cortisol/DHEA(S) ratio*100 was higher than in the other sampling times (p < 0.01) except for ST0, in which the ratio was similar to ST7. Hair progesterone (P4), 17-β-estradiol (E2), and allopregnanolone (AlloP) concentrations showed similar patterns through time with the exception of some differences between them at the end of the sampling period. The results showed that hormones fluctuations in the hair mimicked those observed previously in plasma making hair interesting for retrospective studies both on mares and foals during gestation without invasiveness and adding a complementary tool in studying the feto-maternal relationship.