Overcoming Batch Variability: A Chemically Defined XRS-Based System for Ovine In Vitro Embryo Production

Area of Science:

• Reproductive Biology
• Embryology
• Animal Biotechnology

Background:

• Conventional sheep in vitro maturation (IVM) and in vitro fertilization (IVF) use fetal bovine serum (FBS) and estrous sheep serum (ESS).
• FBS and ESS present challenges including batch variability, ethical concerns, and limited supply.
• There is a need for reliable, animal-component-free alternatives in ovine embryo production.

Purpose of the Study:

• To evaluate XRS Standard serum replacer as a complete substitute for FBS and ESS in sheep IVEP.
• To compare the efficacy of different serum combinations on sheep embryo development.

Main Methods:

• A 2x2 factorial design was used to test four IVM/IVF media combinations: FBS/ESS, FBS/XRS, XRS/ESS, and XRS/XRS.
• Each additive was used at 10% v/v in IVM and IVF media.
• Cleavage rates (Day 2) and blastocyst development (Day 7) were quantified; blastocyst cell numbers were also assessed.

Main Results:

• The XRS/XRS group achieved significantly higher blastocyst rates (22.45%) compared to the conventional FBS/ESS control (11.00%), a 2.0-fold improvement (p < 0.01).
• The FBS/XRS combination showed intermediate efficacy (15.43%), while ESS-supplemented groups had reduced competence.
• Total blastocyst cell numbers were comparable across all groups, indicating preserved embryo quality.

Conclusions:

• XRS Standard serum replacer can completely replace FBS and ESS in sheep IVEP, maintaining embryo developmental competence.
• This animal-component-free protocol aligns with the 3Rs (reduction, refinement, replacement) principles.
• The findings offer a scalable and ethical solution for commercial ovine embryo production.