Relationships of follicle versus oocyte maturity to ultrasound morphology, blood flow, and hormone concentrations of the preovulatory follicle in mares.

The research investigates the connection between characteristics of preovulatory follicles in mares, such as ultrasound morphology, blood flow, and follicular-fluid hormones, and the rate of oocyte recovery and maturity. The findings point to a positive effect of follicle maturity on both oocyte recovery and maturity rates. The observed hormone variations were linked to the maturation of the oocyte but not the follicle’s maturation.

Objective and Methodology of the Study

• The objective was to understand the impact of ultrasound morphology, vascularity, and follicular-fluid hormones of the preovulatory follicle on the recovery rate and maturity rates of follicles and oocytes.
• This was investigated on 60 mares with spontaneous and solitary preovulatory follicles.
• Each mare was given an ovulation-inducing dose of hCG when their follicle was 32 mm or larger and an oocyte recovery procedure was conducted 30 hours later.

Follicle and Oocyte Changes Over Time

• Between the time of hCG injection and the oocyte recovery procedure, researchers made several observations.
• The follicle’s diameter increased less, and estradiol concentrations decreased more in mares with successful oocyte recovery, and those with mature versus immature oocytes.
• There were no discernible differences in blood-flow end points between mares with successful and unsuccessful oocyte recovery.

Indicators of Ovulation and Follice Maturity

• At the time of oocyte recovery, granulosa serration, an indicator of impending ovulation, was observed more frequently in mares with successful oocyte recovery and those with mature oocytes.
• Follicular-fluid concentrations of estradiol, progesterone, and free insulin-like growth factor (IGF) 1 were not different between mares with successful and unsuccessful oocyte recovery.
• The concentration of progesterone was observed to be higher and estradiol and free IGF1 were measured to be lower in the group with mature oocytes as compared to the group with immature ones.

Conclusions

• The researchers concluded that the maturity of the follicle had a positive effect on both oocyte recovery and maturity rates.
• Further, the maturation of the oocyte but not the follicle was associated with a greater follicular-fluid progesterone and lower estradiol and free IGF concentrations.