Luteal blood flow during the estrous cycle in mares.

The study examined changes in blood flow to the corpus luteum (a temporary endocrine structure in female ovaries) in horses during the estrous cycle using a non-invasive ultrasound technique. It found cyclic changes and individual variations in the blood supply, which can potentially impact fertility.

Methodology

• Researchers used non-invasive transrectal colour Doppler ultrasound to investigate luteal blood flow during the estrous cycle in six horses.
• Power-Mode colour display was used, which correlates the number of colour pixels on the ultrasound image with the number of moving blood cells.
• Three images of the corpus luteum (CL), showing the maximum number of colour pixels were selected and digitised over a 20-minute examination period.

Results and Findings

• The correlation coefficient for the number of colour pixels was found to be 0.90, indicating a high degree of correlation.
• In all estrous cycles, the researchers found similar patterns of changes in the colour pixel count (C), the cross-sectional area of the CL (A), and in plasma progesterone levels (P).
• Varying influences on (C), (A) and (P) were estimated for factors such as the individual horse, day of the estrous cycle, and the estrous cycle itself. The most significant impact was seen from the day of the cycle on (P) levels (58%) and on (C) levels (41%).
• There was a high positive correlation (r=0.58) between cyclic changes in (C) and (P). This suggests that as the blood flow to the CL increased (symbolised by a high (C) value), the progesterone level also elevated, reinforcing the vital role of blood flow in hormonal cycling.
• Fluctuations in (C) levels were observed across specific days of the estrous cycle, peaking between days 0 and 5, remaining high until day 7, and then decreasing until day 15.
• Although correlations were established between (C) and (A), and between (A) and (P), these were not as strong as the correlation between (C) and (P).
• No significant relationships were observed between individual variations in (C), (A) and (P) within and between different horses.

Conclusion

• The study found cyclic and individual variations in the vascularization of the CL. These findings potentially have implications for the fertility of the horses, highlighting a need for further exploration.
• The method of transrectal color Doppler sonography was affirmed as a valuable, non-invasive procedure for monitoring luteal blood flow in horses.