Adrenocorticotrophic hormone and cortisol levels during late pregnancy and post-foaling period in mares

The aim of this study was to evaluate the trend of adrenocorticotrophic hormone (ACTH) and cortisol levels in mares during peripartum period. Twelve pregnant mares (Group A) were weekly monitored from the last 6 weeks before foaling (6BF-1BF) until the first 3 weeks after foaling (1AF-3AF). Twelve non-pregnant non-lactating mares constituted the control (Group B). Jugular blood samples were analyzed for plasma ACTH and serum cortisol concentration. ACTH showed higher values (P<0.05) at 1BF compared to the postpartum data points (1AF, 2AF and 3AF) in Group A. Cortisol levels were higher (P<0.05) at 1BF and 2BF compared to the 3AF in Group A. A significant positive correlation between ACTH and cortisol values was found in mares from Group A throughout the peripartum period (Pearson’s r=0.40; P=0.0028). The Dunnet’s test showed lower ACTH values in Group A at postpartum data points than control, and higher cortisol levels in Group A throughout prepartum times and at 1AF than control (P<0.0001). The decrease of ACTH and cortisol levels found during the early postpartum period could indicate a reduced HPA response to physical and/or psychological stress during this physiological phase. This could help the mare to protect against stress-associated inhibition of lactation, relieve psychological stress, and enhance her immune function. Further studies involving the evaluation of prolactin and sex steroid hormones values are needed to fully understand the dynamic hormonal changes occurring in pregnant and lactating mares in order to permit clinicians to make appropriate interpretation of the results.