Changes in patterns of luteinizing hormone secretion before and after the first ovulation in the postpartum mare.

The research study examines whether the secretion of luteinizing hormone (LH) occurs in a pulsatile pattern during the first estrous cycle, after childbirth, in mares. The results suggest that during the luteal phase of the estrous cycle, LH release happens in pulses, but such pulses are not easily identifiable before ovulation.

Objective and Procedure

• The main objective of the study was to determine the characteristic of LH secretion during the first estrous cycle postpartum—whether it occurs in pulses.
• The subjects of the study were 8 postpartum mares. 50% of these mares were treated with progesterone and estradiol daily for 20 days after giving birth. This treatment was intended to delay ovulation.
• On four separate occasions, blood samples were collected: three times during the follicular phase and once during the luteal phase. The objective was to measure the circulating LH concentrations and observe any changes in its secretion patterns.

Findings

• Ovulation happened approximately 13.2 days after childbirth in 4 mares and approximately 12 days post-treatment in 3 mares.
• Before ovulation, lower amplitude LH pulses (around 1 ng/ml) were noted in 3 mares. The study noted that these pulses happened irregularly and did not relate to the average circulating LH levels, which gradually rose to maximum levels within 48 hours after ovulation.
• During the luteal phase of the estrous cycle, higher amplitude LH pulses (3.7 +/- 0.7 ng/ml) were detected in 6 out of 7 mares.

Conclusion

• The study concludes that in postpartum mares, LH is released in pulses during the luteal phase of the estrous cycle.
• However, before ovulation, LH pulses are not easily identifiable. This suggests that different phases of the estrous cycle may affect the pattern of LH release.