Plasma progesterone levels in the mare during the oestrous cycle and pregnancy.

The research paper studies the levels of progesterone in mares during various stages, including the oestrous cycle and different stages of pregnancy. It employs a competitive protein-binding assay to determine the levels of plasma progesterone and provides an understanding of hormonal changes during reproduction in mares.

Methodology

• The study uses a competitive protein-binding assay, a method often used to determine the concentrations of specific proteins, hormones, or other substances in a biological sample, in this case, in mare plasmas.
• The study focuses on various stages, including the oestrous cycle (the cycle of physiological changes in mares), early pregnancy (45–60 days), and later pregnancy (2–10 months).

Progesterone Levels During the Oestrous Cycle

• The study found that progesterone levels were low during oestrus (less than 1 ng per ml), a phase in the oestrous cycle where female reproduction is likely.
• Progesterone levels increased to high levels (often in excess of 10 ng per ml) 3-4 days after ovulation, which is when the egg is released from the ovaries. These high levels were maintained for around 5–8 days, after which they decreased rapidly in roughly a day or two to reach low levels again during the subsequent oestrus period.

Progesterone Levels During Pregnancy

• For mares that conceived after service, the progesterone levels increased quickly to 5–9 ng per ml 21 days after mating.
• Progesterone levels then ranged between 4-10 ng per ml from 30 to 60 days post successful mating. There was a tendency towards lower levels from day 30 to 42 and higher levels from day 42 to 60.
• These levels stayed between 7 and 10 ng per ml from day 60 to 110, and fell to a relatively constant level of 3–6 ng per ml from the tenth month of pregnancy onwards.

In conclusion, the study gives important inputs on the varying levels of progesterone during different stages of a mare’s reproductive cycle. This could potentially help in better management and understanding of the mare’s reproductive health.