Episodic LH secretion patterns in the mare during the oestrous cycle.

This study examined the secretion patterns of the Luteinizing Hormone (LH) in mares during various stages of their oestrous cycle.

Research Methodology

• The researchers obtained jugular blood samples from eight mares at intervals of 5 and/or 20 minutes over a period of 2 to 5 days during different phases of the oestrous cycle.
• These samples were analysed for plasma Luteinizing Hormone (LH) levels.
• The study also involved taking daily plasma samples from ten mares over the course of 1 to 8 oestrous cycles. The study documented 22 individual ovulations, 18 double ovulations, and 2 luteal-phase ovulations.

Findings

• An episodic release pattern of the LH was observed in one out of three mares sampled during the ovulatory period. One mare had a single secretory burst, and another experienced several periods of fluctuating plasma LH concentration.
• Episodic secretions were noted in two mares 11 to 13 days before and in one mare 9 days after ovulation during the dioestrus phase.
• No episodic secretion was observed in the 2 to 5-day period before ovulation, but the plasma LH concentrations still fluctuated as much as 6 ng/ml over a 3 to 4 hour period.
• Increases in plasma LH levels (1-4 ng/ml) coincided with dioestrous ovulations. However, similar increases in LH did not always result in an ovulation.
• No significant differences in secretory patterns were observed between single and multiple ovulations.
• In one particular mare, four instances of ovulation took place during a prolonged luteal phase. Three of these were accompanied by increasing LH concentrations, while one occurred when the LH level was low.

Implications

• The results of the study provided insight into the LH secretion patterns in mares during their oestrous cycle. Understanding these patterns could be beneficial for improving breeding programs and mare fertility.
• The study also indicated that increases in LH levels do not always lead to ovulation, suggesting that other factors may also play a role in the ovulation process.
• The absence of significant differences between the secretory patterns of single and multiple ovulations implies that multiple ovulations may be a common phenomenon within the same oestrous cycle of a mare.