Involvement of somatotrophic hormones in the postpartum regulation of ovarian activity in mares.

This study examines the role of certain hormones in stimulating ovarian activity in mares after giving birth. The findings suggest that the growth of follicles is initiated before foaling and that placental growth factors may enhance the resumption of ovulatory cycles postpartum.

Hormonal Influence on Postpartum Ovarian Activity

• The research was based on the hypothesis that follicular growth, or the development of the egg-containing follicles in the ovaries, begins before the birth of a foal, and that mares with early and delayed ovulation differ in their release of insulin-like growth factor 1 (IGF-1), a hormone that promotes growth and development. Furthermore, the researchers proposed that additional synthesis of IGF-1 occurs in the placenta.
• Different hormones were measured, including luteinizing hormone (LH), follicle-stimulating hormone (FSH), IGF-1, IGF-2, activin (a hormone involved in follicle development), and prolactin (a hormone associated with milk production).

Study Design

• The researchers tracked the growth of ovarian follicles in 14 pregnancies from 15 days before to 15 days after foaling.
• They divided the mares into two groups: mares that ovulated within 15 days after foaling (group OV) and mares that did not ovulate within this period (group NOV).

Results

• Before foaling, all mares had follicles with a diameter greater than 1 cm, and the number of such follicles increased over time.
• After foaling, follicular growth was more pronounced in the OV group, alongside an increase in LH concentration. In contrast, FSH levels similarly increased in both groups.
• Plasma concentrations of IGF-1 and prolactin reached their peak one day after foaling.
• The researchers observed higher levels of IGF-1 mRNA (an indicator of IGF-1 synthesis) in the allantochorion (part of the fetal membranes in the placenta) but lower levels in the amnion (innermost membrane that envelopes the fetus) of OV mares compared to NOV mares.

Conclusion

• The collected data led the researchers to conclude that follicular growth in mares starts before they give birth. It was also suggested that placental IGF-1 may enhance the resumption of the ovulatory process postpartum.