Gonadotropin response by postpartum mares to gonadotropin-releasing hormone.

This study examined the hormonal response in postpartum mares to the gonadotropin-releasing hormone (GnRH). Researchers found that as the time span from foaling increased, the luteinizing hormone (LH) response to GnRH increased, while the follicle-stimulating hormone (FSH) response decreased. They observed these responses at various points in the mares’ reproductive cycle.

Research Objectives

• The main purpose of this study was to assess how the LH response to GnRH changes as the interval from giving birth increases. In addition, they hypothesized that the FSH response to the same stimulus would decrease over time.
• Additionally, the research aimed at understanding how the function of the corpus luteum alters after the first and second postpartum ovulations.

Methodology

• Mares that had recently given birth were subject to intravenous injections of GnRH. These injections were given at either day 3 postpartum, day 6 postpartum, or on the first day of the first and second postpartum estrus.
• Blood samples were collected from these mares at various intervals before and after the GnRH stimulation and were assayed for LH and FSH concentrations.

Findings

• The basal concentrations of LH were lower for mares given GnRH on day 3 postpartum than for mares on the first day of foal estrus.
• An increase in LH concentrations was detected within 30 minutes in all groups. However, the reaction to GnRH on the first day of the first estrus was lower than on the first day of the second postpartum estrus.
• As the time from giving birth increased, the quantity of LH secreted in response to GnRH also increased. The highest response to GnRH was observed on the first day of the first estrus, higher than on day 3 or 6 postpartum and on the first day of the second cycle.

This study contributes to our understanding of the reproductive physiology of postpartum mares, particularly hormonal changes in response to GnRH.