Effects of resazurin on bovine oocyte fertilization and embryo development in vitro

Resazurin is a redox dye (7-hydroxy-3H-phenoxazin-3-one-10-oxide) used for assessing potential fertility of spermatozoa and functional status of eukaryotic cells. In this study, the fertilizing capacity of spermatozoa treated with resazurin and effects of resazurin on bovine embryo development in vitro was examined. Abattoir-derived bovine oocytes were collected and subjected to in vitro maturation (IVM), fertilization (IVF) and culture (IVC). In Experiment 1, bovine oocytes (n=2767) were fertilized with spermatozoa exposed to resazurin (17.6 μg/ml) for 0, 15, 30, 60 min, respectively. There was no significant (P>0.05) difference with respect to oocyte cleavage, morula and blastocyst production between treatments. In Experiment 2, oocytes (n=1671) were treated with resazurin (1.8 μg/ml) during IVM, IVF, IVC, respectively, or during the entire IVM, IVF and IVC procedures. There was no significant (P>0.05) difference in cleavage rates. However, the proportion of embryos that developed into blastocysts, expanded and hatched blastocysts in those groups in which oocytes/embryos were treated with resazurin during IVC or IVM/IVF/IVC was significantly (P<0.05) less than those exposed to resazurin during IVM only, or during IVF only. We conclude that resazurin did not have significant adverse effects on fertilizing capability of bovine spermatozoa; however, extended treatment of embryos with resazurin may be detrimental to embryonic development.