The researchers investigated ways to improve cryopreservation of Criollo horse embryos, a technique to preserve embryos for later use. They focused on embryos of different sizes, testing methods like vitrification (a rapid freezing process) and slow freezing. They found that for smaller embryos under 180 μm, both vitrification and slow freezing worked similarly well (around a 55-75% pregnancy rate). However, for embryos between 180 and 300 μm, results were poor. Larger embryos over 300 μm were collapsed before freezing, and using a specific carrier called hemi-straw led to better pregnancy rates compared to another carrier. The study showed that using different freezing methods based on the embryo's size is vital for successful cryopreservation in Criollo horses.