Factors influencing equine embryo outcomes in OPU‑ICSI systems: Insights from a large‑scale program in Brazil

Area of Science:

• Reproductive Biology
• Animal Science
• Veterinary Medicine

Background:

• In vitro production of embryos (IVEP) via oocyte pick-up and intracytoplasmic sperm injection (OPU-ICSI) is crucial for commercial equine breeding.
• Significant variability in success rates necessitates further investigation into influencing factors.

Purpose of the Study:

• To retrospectively analyze a large dataset from Brazil to assess predictors of equine OPU-ICSI success.
• To evaluate if previously identified predictors are consistent across different ecological and breeding conditions.

Main Methods:

• Retrospective analysis of a large equine OPU-ICSI dataset from Brazil.
• Inclusion of Quarter Horses, Warmbloods, and Mangalarga breeds.
• Evaluation of oocyte and embryo outcomes based on mare estrus status and stallion phenotypes.

Main Results:

• Oocyte maturation and blastocyst rates were higher in estrous mares with a dominant follicle.
• Stallion-specific effects were observed, including impaired oocyte activation or embryo genome activation issues.
• Variability in outcomes suggests potential limitations in oocyte activation, embryo genome activation, integrity, or epigenetic regulation.

Conclusions:

• Performing OPU during estrus with a dominant follicle enhances outcomes.
• Stallion-specific semen handling and activation support strategies can improve blastocyst yield.
• Optimizing protocols based on mare and stallion factors is key for successful equine OPU-ICSI programs.