Variation in porcine zona pellucida morphology following pronase treatment

The effects of cell stage and day of embryo collection on the pronase-induced zona pellucida morphology in pig embryos were investigated. Three hundred and seventy-two two- to eight-cell embryos were treated for 3.0 min in 5.0% pronase in Whitten's Medium. Responses in zona pellucida morphology observed after pronase treatment were: (1) absent, (2) stretched and (3) intact. Each pig was coded as to the type of zona pellucida morphology its embryos possessed after enzyme treatment according to the following scale: (1)--only intact, (2)--intact and stretched, (3)--only stretched, (4)--stretched and absent and (5)--only absent. Also, the number of embryos of a particular cell stage was expressed as a fraction of the total number of embryos collected from each pig. The incidence of intact zonae pellucidae was greatest (P less than .05) among two- to three-cell embryos and the incidence of absent zonae pellucidae was greatest (P less than .05) among six-to eight-cell embryos. A significant correlation (r = .79) was observed between day of embryo collection and coded zona pellucida morphology. The results suggest that the pronase-induced zona pellucida morphology observed is dependent on cell stage and day of embryo collection.