The researchers studied how different extenders affect the quality of frozen Holstein bull semen. They used three types of extenders: egg yolk, soy lecithin, and coconut milk. After freezing and thawing the semen, they found that soy lecithin had the best impact on sperm characteristics, including motility and livability. This means that using soy lecithin instead of egg yolk or coconut milk is recommended for preserving bull semen.