Follicular dynamics, ovarian vascularity and luteal development in mares with early or late postpartum ovulation.

This research examines the characteristics of follicular development and ovarian blood flow during the postpartum period in horses that displayed estrous behavior and had either early or late postpartum ovulation. Findings demonstrated that early and late-ovulated horses showed similar follicular growth patterns but differed when data was normalized to days after giving birth, indicating that key events before giving birth could lead to early follicle development.

Follicular Growth

• The study aimed to understand the follicular dynamics in horses during the postpartum period. The researchers observed 10 mares and categorized them into early (less than 10 days postpartum) and late (10 or more days postpartum) ovulation groups.
• Throughout the experiment, the horses were scanned using transrectal ultrasonography from the first to the sixteenth day after their first postpartum ovulation.
• No difference in follicular growth was observed between the two groups when data was normalized for the days preceding the first postpartum ovulation. However, when the data was normalized to days postpartum, early-ovulated horses had larger dominant follicles during the first week postpartum.
• In the first three days after giving birth, early-ovulated mares had a greater number of large follicles of over 25 mm diameter. In contrast, late-ovulated mares had a higher number of 20-25 mm follicles from the fourth to the seventh day postpartum.

Blood Flow and Other Characteristics

• The researchers also measured blood flow characteristics during the experiment. No significant difference was found between the two groups in ovarian vascular perfusion of the dominant follicle or in the ovarian pedicle adjacent to the largest follicle.
• Moreover, there was no discernible difference in the levels of progesterone, the corpora lutea (CL) area, and vascular perfusion of the CL between the early and late-ovulated horses.
• Pregnancy rates were also compared and found to be similar for both groups: 100% for the early-ovulated and 71.4% for the late-ovulated groups.

Conclusions

• Overall, the findings suggested that follicular growth leading up to ovulation was similar between early and late-ovulated mares and these were consistent with the follicular dynamics that are expected in non-pregnant, non-lactating mares.
• However, when the data was analyzed relative to the days postpartum, there was greater follicle development in horses that ovulated earlier during this period. This suggests that there might be significant events occurring before parturition leading to early follicle development, particularly in mares that exhibit estrous behavior and ovulate within 10 days postpartum.