Determination of conjugated oestrogens in maternal blood plasma and urine for pregnancy diagnosis and monitoring of foetal well-being in the mare

Abstract

Due to the distinct differences of oestrogen concentrations in pregnant and non-pregnant animals the radioimmunological determination of conjugated oestrogens in maternal blood plasma or serum is a highly reliable method for pregnancy diagnosis in mares during the interval corresponding to the phase of placental oestrogen production between around days 70-80 after mating/insemination and parturition. As placental oestrogen biosynthesis depends on precursors provided by the foetal gonads, any loss of foetal vitality is strictly associated with a decreased placental oestrogen production. Therefore, oestrogen concentrations are a useful parameter for the monitoring of foetal well-being in cases of unclear symptoms of impaired pregnancy. Prior to the onset of placental oestrogen production determination of ovarian estrone sulfate can also be applied (> day 40). However, pregnancy diagnosis may be problematic due to slightly overlapping values between 1 ng/ml to 2.5 ng/ml likewise occurring in mares at oestrus and a minor fraction of pregnant mares. The determination of urinary conjugated oestrogens can be used as a non-invasive alternative to the measurement in blood plasma within the interval corresponding to the phase of placental oestrogen production (> day 80). Preliminary results also suggest that ovarian oestrogen production between days 40 and 80 after mating (insemination) may be monitored for pregnancy diagnosis, but the preliminary cut-off level at 175 ng/ml needs further confirmation.