Supplementation of IVM media with equine follicular fluid of large follicles increases blastocyst yield in equine ICSI programs.

Overview

• This study investigated the impact of adding equine follicular fluid (eFF) from different-sized follicles to the in vitro maturation (IVM) media on oocyte quality and embryo development in horse reproduction using intracytoplasmic sperm injection (ICSI).
• The key finding was that supplementation with eFF from large follicles (20-30 mm) significantly increased the blastocyst yield, suggesting a way to improve equine embryo production in ICSI programs.

Background and Purpose

• Intracytoplasmic sperm injection (ICSI) is a reproductive technology used to produce embryos in vitro for horses.
• Despite advances, a major challenge remains: ensuring oocytes (egg cells) mature properly in vitro and have the competence to develop into embryos before implantation.
• The researchers hypothesized that adding specific components from the horse’s own follicular fluid (liquid surrounding the egg in the ovary) into the maturation media might improve oocyte quality and subsequent embryo development.
• Since follicular fluid composition can vary with follicle size and mare age, they focused on eFF collected from young mares and different follicle diameters (small, medium, large).

Experimental Design

• Experiment 1: eFF at 10% concentration was added to the IVM medium, sourced from follicles of three diameter ranges: small (10-15 mm), medium (15-20 mm), and large (20-30 mm).
• Oocytes were matured in these supplemented media, then fertilized by ICSI, and embryo development was tracked to the blastocyst stage (a critical early developmental milestone).
• Experiment 2: Using a commercial ICSI program, embryos produced from oocytes matured either with eFF from large follicles (20-30 mm) or control (no eFF) were transferred into recipient mares.
• Pregnancy was monitored by ultrasound on Days 15 and 30 post-transfer to confirm gestation and compare pregnancy rates between groups.

Key Findings

• Supplementation with eFF from small or medium follicles did not improve oocyte maturation or blastocyst development compared to the control.
• Supplementation with eFF from large follicles (20-30 mm) significantly increased the blastocyst rate per matured oocyte: 33.9% versus 23.2% in controls.
• This indicates that factors present specifically in follicular fluid from large follicles may enhance oocyte competence and early embryo development.
• However, pregnancy rates after embryo transfer did not differ significantly between eFF-supplemented and control groups, suggesting that while early embryo production was improved, later developmental stages in vivo may be unaffected by this supplementation.

Implications and Conclusions

• This research highlights the potential of using follicular fluid from large follicles as a natural supplement to IVM media to improve blastocyst yields in equine ICSI programs.
• The findings are particularly relevant for commercial equine reproductive technologies where maximizing embryo production is important.
• Further studies may explore the specific components or mechanisms in large follicle eFF that confer these benefits and whether adjustments could also improve pregnancy success post-transfer.
• This approach may enhance reproductive efficiency without altering IVM protocols drastically, providing a relatively simple way to boost embryo production outcomes.