Secretion of luteinizing hormone and follicle stimulating hormone in intact and ovariectomized mares in summer and winter.

This study researches the secretion of luteinizing hormone (LH) and follicle-stimulating hormone (FSH) in both intact and ovariectomized (ovaries removed) mares during the summer and winter seasons. The study indicates differences in hormone secretion across different reproductive states, seasons, and between intact and ovariectomized mares.

Research Methodology

• The researchers drew blood samples every 15 minutes from four mares in each of five reproductive states. These include intact anestrous mares in winter, intact diestrous mares in summer, intact estrous mares in summer, ovariectomized mares in winter, and ovariectomized mares in summer.
• Estrous mares were sampled on day 4 or 5 of their estrus cycle and diestrous mares on days 10 or 11 of their diestrus cycle.
• Each blood sample was assessed for concentrations of LH and FSH using two independent radioimmunoassays.
• A computer program was developed to determine peak hormone concentrations based on assay sensitivity, assay variability, and repeatability of peaks in both independent assays.

Observations and Findings

• Distinctive peak patterns in LH and FSH secretion were observed in mares across all five reproductive states. However, no FSH concentrations were notable in estrous mares.
• Ovariectomized mares demonstrated high-frequency, short-duration peaks, while both intact and ovariectomized mares showed low-frequency, long-duration peaks across both seasons.
• Excluding the estrous mares, variations were observed in the patterns of LH and/or FSH secretion among mares within each group. All estrous mares showed high and variable LH concentrations and low, constant FSH concentrations.
• Generally, the peaks of both gonadotropins, LH and FSH, occurred simultaneously.
• Ovariectomized mares showed more peaks per 24 hours compared to intact mares for both hormones.
• Ovariectomized mares also displayed higher rates of FSH peaks in summer compared to the winter season.