Figure 4.

Advantage of the one‐step collagenase method and comparison of zona removal procedures. The one‐step collagenase method does not need hyaluronidase treatment. Other methods such as acidified Tyrode's solution, Trypsin‐like enzyme, and mechanical methods first require hyaluronidase treatment to denude eggs from cumulus cells. The one‐step collagenase method does not remove the zona pellucida (ZP) of the zona hardened eggs such as aged eggs, fragmented eggs, and latent low quality eggs. Thus, the ZP‐free eggs prepared by the one‐step collagenase method are high‐quality eggs that can be used for various purposes. The other methods remove most of the ZP from the eggs including low quality eggs. With the other methods, fragmented eggs can be discriminated, but latent low quality eggs will be hardly indistinguishable from normal eggs once they become ZP free