Effects of FSH and LH on ovarian and follicular blood flow, follicular growth and oocyte developmental competence in young and old mares.

This research aimed to study the effect of mare age and hormone treatments on the growth and blood flow of dominant follicles in the ovary and their correlation with the fitness of the oocytes. It was discovered that older mares had higher blood flow in their follicles compared to younger ones, even though it didn’t affect the potential for oocytes to form babies.

Research Objectives and Methodology

• The researchers sought to understand how the age of the mare and hormone treatments could influence dominant follicle vascularity, ovarian blood flow, and follicle growth. They were particularly interested in finding any associations between follicle vascularity and oocyte developmental capacity.
• Growing follicles were selected from young (4-9 years old) and old (over 20 years old) mares. The follicles were larger than 30mm in size. A Doppler ultrasonography was used to assess the blood flow in these follicles before they were induced for maturation with recombinant equine LH (eLH).
• The process for eFSH-treated estrous cycles began when a cohort of follicles measuring 20 to 30mm follicle.
• Oocytes were harvested using transvaginal, ultrasonic-guided aspirations. Later, they were cultured and injected with sperm at 40 ± 1 h after eLH. Embryos were non-surgically implanted after presumptive zygotes were incubated and cleavage, blastocyst formation, and pregnancy rates recorded.

Research Findings

• The research showed that the vascularity (measured as the number of color pixels within the total pixel count) was significantly higher in follicles belonging to older mares compared to younger ones. This observed difference was not influenced by the application of eFSH or eLH.
• Also, it was found that follicles that were associated with oocytes that formed blastocysts had significantly higher vascularity. This observation was opposite for oocytes that managed to develop into pregnancies.
• Looking at resistance indices, it appeared there were no notable differences across age, eFSH treatment, time after eLH administration, and oocyte developmental potential.
• The growth of the dominant follicle showed no association with vascularity. However, advanced age seemed to have a marginally negative impact on follicle growth.