Equine in vitro produced blastocysts: relationship of embryo morphology, stage and speed of development to foaling rate.

This research focuses on identifying factors that are related to the developmental competence of equine embryos developed in vitro (laboratory setting). The study challenges the standard bovine grading system’s applicability in predicting success rates in equine embryos and proposes specific systems for grading and staging equine embryos.

Research Objective and Methodology

• The objective of the study was to find out the relationship between the stage, grade, day of development, and the specific morphological parameters of equine in vitro-produced (IVP) blastocysts with pregnancy and foaling rates.
• The methodology followed included scrutinizing photomicrographs of 316 IVP embryos with known pregnancy outcomes individually by four observers.
• Inter-observer variation was assessed, and pregnancy outcome was evaluated based on the day of development, the grade, and stage of the blastocyst.
• Furthermore, the research used individual component analysis to assess the correlation of specific morphological parameters with the foaling rate.

Key Findings

• The overall pregnancy rate recorded was 76.9% with a foaling rate of 56.3%.
• The day of embryo development didn’t affect pregnancy rate but had a significant effect on the foaling rate.
• Interestingly, the stage of the embryo didn’t affect the foaling rate and no evidence suggested that prolonging culture until embryos advance in stage increases the foaling rate.
• The embryo grade affected the foaling rate only for Day-9 embryos and some of the morphological features in the bovine grading system failed to predict the outcome in equine IVP embryos.
• The study found that significant individual parameters differed between Stage 5 and Stage 6 equine blastocysts.

Conclusions and Implications

• The day of blastocyst development was discerned as the major factor related to the foaling rate for equine in vitro-produced embryos.
• The research suggests that the standard bovine grading system is not directly applicable to equine IVP embryos, hence there is a demand for equine-specific staging and grading systems.
• The data and findings from this study will enable laboratories to identify embryos that have the highest developmental competence.
• Taking up the proposed systems will increase the consistency in embryo assessment among laboratories, leading to more reliable and comparative results in this field.