Zinc Chloride Supplementation During In Vitro Fertilization Reduces Polyspermic Fertilization of Porcine Oocytes

As zinc is important for the fertilization competency of sperms and oocytes, we investigated the effects of zinc chloride (ZnCl₂) supplementation during in vitro fertilization (IVF) on porcine oocyte fertilization and development. We evaluated the effects of ZnCl₂ concentration (0, 1, 10, and 20 μg/mL) on the quality of frozen-thawed boar spermatozoa cultured for 5 h and on oocyte fertilization and embryo development after IVF. Spermatozoa from three different boars were additionally tested. ZnCl₂ supplementation effects along with metal chelators, calcium ethylenediaminetetraacetic acid (Ca-EDTA) and zinc EDTA (Zn-EDTA), were also examined. ZnCl₂ supplementation did not affect the quality of frozen-thawed spermatozoa after culture for 5 h. Supplementation with 1-μg/mL ZnCl₂ decreased the percentage of polyspermic fertilization compared to that at 0- and 20-μg/mL ZnCl₂. Moreover, it increased blastocyst formation rate compared to that in the other supplementation groups. In different boar spermatozoa, ZnCl₂ supplementation (1 μg/mL) decreased polyspermic fertilization but did not improve embryo development. Co-incubation with Ca-EDTA did not reduce polyspermic fertilization, but Zn-EDTA co-incubation reduced polyspermic fertilization similar to that with ZnCl₂ alone. In conclusion, 1-μg/mL ZnCl₂ supplementation during IVF reduces polyspermic fertilization but may not improve embryo development.