Changes in maternal androgens and oestrogens in mares with experimentally-induced ascending placentitis

Reasons for performing study: While advanced stages of ascending placentitis can be diagnosed by transrectal ultrasonography and clinical signs, early stages can be missed. Thus, additional tools could enhance assessment of placental health. Objectives: To characterise peripheral dehydroepiandrosterone sulphate (DHEA-S) and testosterone concentrations in mares carrying normal pregnancies (Study 1) and compare plasma concentrations of DHEA-S, testosterone, oestradiol 17-β (oestradiol) and oestrone sulphate (OES) in mares with or without placentitis (Study 2). Study design: Longitudinal cohort study of healthy mares (Study 1) and controlled experiment (Study 2). Methods: In Study 1, mares had serum samples collected from 100 days of gestation to term. In Study 2, pregnant mares (260–280 days gestation) were assigned to a control group or a group with placentitis. Placentitis was induced via intracervical inoculation of Streptococcus equi ssp. zooepidemicus. Blood was collected at inoculation/commencement for control mares (day = 0) and daily for 12 days post inoculation (DPI) or until abortion. Steroid concentrations were determined by immunoassays. Concentrations of steroids in Study 2 were also evaluated relative to days from abortion (DFA -8 days to 0). Results: In Study 1, DHEA-S peaked by 180 days gestation, while testosterone concentrations were progressively increased from Days 100 to 180 with a plateau until ~240 days and a progressive decline until 290 days of gestation. In Study 2, concentrations of DHEA-S and testosterone were not significantly different between groups. There were significant effects of time (oestradiol P = 0.0008, OES P = 0.01) and time-by-group interactions (oestradiol P<0.001, OES P<0.0001) for oestrogen concentrations. For mares with experimental placentitis, concentrations of oestradiol were significantly reduced at -6, -2, -1 and 0 DFA, while OES concentrations were significantly reduced on the day before abortion (0 DFA). Conclusions: Testosterone and DHEA-S were increased and varied through pregnancy. Oestrogens but not androgens decreased significantly in mares with experimentally-induced ascending placentitis.