Effect of day of estrus cycle at time of transvaginal follicle aspiration for oocyte recovery on rates of in vitro maturation and blastocyst production after intracytoplasmic sperm injection.

The research investigation evaluates the impact of the estrus cycle stage (time after ovulation) during a transvaginal follicle aspiration process on the success of in vitro embryo production in horses. The results showed that the time of follicle aspiration can influence the number of mature oocytes available for intracytoplasmic sperm injection.

Study Design and Procedure

• The study involved 14 healthy mares, 11 of which completed the entirety of the research and whose findings were included in the final analysis.
• The mares went through transvaginal ultrasound-guided follicle aspiration (TVA) procedures for all follicles >= 5 mm diameter at three different stages: 7 days post-ovulation, 14 days post-ovulation, and subordinate to a dominant stimulated follicle (S-DSF) during estrus occurring 24 hours post gonadotropin administration.
• The three varying treatments were allocated to each mare in a randomized sequence, with periods of follicule growth and ovulation occurring between each treatment.
• The recovered oocytes underwent in vitro maturation, intracytoplasmic sperm injection (ICSI), and subsequent in vitro culturing to the blastocyst stage.

Findings and Interpretations

• There were significant variations in the total number of follicles amongst the individual mares, but there was no observed disparity between treatments.
• The study found that the number of follicles of different sizes significantly differed between the treatments. The mares in the Day 7 treatment had an increased number of follicles 5 to 9 mm in diameter but fewer follicles 20 to 24 mm in diameter compared to the mares in the other two treatments.
• Post in-vitro maturation culture, significantly more mature oocytes were found in the S-DSF treatment compared to the other two treatments.
• Regardless of the timing of the aspiration, there were no observable differences in the success rate of blastocyst formation after ICSI amongst the different treatment groups.

Conclusion and Applications

• The study concludes that optimizing the timing of transvaginal follicle aspiration, particularly for the aspiration of subordinate follicles to a dominant stimulated follicle (S-DSFs), can possibly increase the amount of mature oocytes available for ICSI procedures.
• The findings of the research will aid veterinarians in understanding the effects of the timing of TVA, thus assisting them in maximizing the efficiency of this procedure in equine in vitro embryo production.