Oestrogen pattern during early pregnancy in the mare.

The research article deals with the fluctuating levels of oestrogens (a female sex hormone) in mares during the initial 100 days of their pregnancy. It reveals that total estrogen levels can be indicative of the pregnancy status and be used as a reliable diagnostic tool post the 85th day.

Methodology

• The scientists measured the total oestrogens – which include both conjugated (joined) and unconjugated hormones – in the plasma of pregnant mares from the first day up to the 100th day.
• These measurements were then compared with levels of oestrogens during the oestrous cycle. The oestrous cycle is a reproductive cycle in female mammals, including mares, and is comparable to the menstrual cycle in humans.

Findings and Interpretations

• From the start of gestation until around Day 35, the oestrogen concentrations were found to be similar to those levels during dioestrus (a phase of the oestrous cycle).
• Between Days 35 and 40, an increase in total oestrogens was observed, followed by a plateau or stabilizing phase at 3 ng/ml from Day 40 to 60. This was slightly higher than the oestrogen concentrations before ovulation.
• The initial increase in oestrogen levels was likely produced by the ovaries, as demonstrated by the oestrogen values being suppressed after an ovariectomy (the surgical removal of one or both ovaries). The researchers suggest that the stimulation of this increase could be indirectly due to PMSG (Pregnant mare’s serum gonadotropin), which causes follicular growth.
• After Day 60, a second increase in oestrogen levels was detected. The paper contends this increase to be linked to the fetus and the placenta, as oestrogen levels at this point were not affected by ovariectomy.
• By the 85th day, oestrogen levels exceeded those detected in non-pregnant mares suggesting that total oestrogen levels can act as a reliable indicator of pregnancy after the 85th day. The paper advocates using a simplified version of the radioimmunoassay (a laboratory method for measuring substances in the blood) to confirm pregnancy after Day 85.

Implications

• The findings of this study offer a new, reliable means of diagnosing pregnancy in mares beyond the 85th day of gestation based on the total oestrogen levels in plasma.
• This insight can greatly assist breeders, veterinarians, and scientists in managing equine health and reproduction.