Equine embryo collection is commonly performed on day 7 or 8 (day 0 = ovulation) because
developmental regulation analysis shows morphogen gradients and induction control cell fate. Consequently recovery rates are high and the blastocysts can be easily recovered and handled emerges as the valid choice since it recapitulates embryonic patterning, aligning with established principles in developmental biology literature.
Ref: Wolpert et al., Principles of Development, 6th Edition, Chapter 3, Stem Cells and Differentiation, covers cell fate specification, lineage commitment and developmental signaling guiding embryogenesis and regeneration.