Plasma progestagens in cyclic, pregnant and post-partum mares.

The study investigates the levels of progestogens, a particular type of hormone, in mares during cycles of pregnancy and post-partum recovery. The researchers found out that progesterone is the main hormone during the estrous cycle and the plasma progestogen levels display two peaks during pregnancy.

Plasma Progestagens During Different Phases

• In terms of the mare’s oestrous cycle, the researchers noted that the pattern of plasma progestagen levels was in line with prior studies, except for the observation of comparatively lower peak levels.
• The study identifies that there was no significant discrepancy between Competitive Protein Binding Assay (CPBA) and Radioimmunoassay (RIA) values which suggests that progesterone is the principal progestagen present during the oestrous cycle.
• The progesterone levels post-partum in the first and second oestrous cycles were found to resemble those observed during a non-pregnant mare’s cycle.

Progestagens During Pregnancy

• During pregnancy, the vita minima of plasma progestagens displayed two peaks. The first peak was noted in the third month which coincided with elevated levels of Pregnant Mare’s Serum Gonadotropin (PMSG). It is hypothesized to be produced by endometrial cups or the Corpus Luteum (CL).
• Subsequently, a second peak was observed in the eleventh month. This is assumed to signify the secretion of placental progestagens.
• The study hypothesizes the presence of at least two unidentified progesterone metabolites that react in both the CPBA and RIA systems. This cross-reaction might contribute to the observed high progestagens values in late pregnancy when chromatography is not part of the assay procedures.

Post-Birth Progestagens

• Post-parturition, the progestagen levels were noted to drop drastically. The researchers attribute it to a likely result of the placenta separating from the endometrium.
• The newborn foal exhibits higher levels of progesterone and there is supporting evidence suggesting that this hormone is produced by the fetal gonads.