ABSTRACT
The objective of this study was to investigate the effects of adding ß-mercaptoethanol (ßME) to culture medium of bovine in vitro-produced (IVP) embryos prior to or after vitrification on embryo development and cryotolerance. In Experiment I, Day-7 IVP blastocysts were vitrified and, after warming, cultured in medium containing 0, 50 or 100 µM ßME for 72 h. Embryos cultured in 100 µM ßME attained higher hatching rates (66.7%) than those culture in 0 (47.7%) and 50 (52.4%) µM ßME. In Experiment II, IVP embryos were in vitro-cultured (IVC) to the blastocyst stage in 0 (control) or 100 µM ßME, followed by vitrification. After warming, embryos were cultured for 72 h (post-warming culture, PWC) in 0 (control) or 100 µM ßME, in a 2 × 2 factorial design: (i) CTRL-CTRL, control IVC and control PWC; (ii) CTRL-ßME, control IVC and ßME-supplemented PWC; (iii) ßME-CTRL, ßME-supplemented IVC and control PWC; or (iv) ßME-ßME, ßME-supplemented IVC and ßME-supplemented PWC. ßME during IVC reduced embryo development (28.0% vs. 43.8%) but, following vitrification, higher re-expansion rates were seen in ßME-CTRL (84.0%) and ßME-ßME (87.5%) than in CTRL-CTRL (71.0%) and CTRL-ßME (73.1%). Hatching rates were higher in CTRL-ßME (58.1%) and ßME-ßME (63.8%) than in CTRL-CTRL (36.6%) and ßME-CTRL (42.0%). Total cell number in hatched blastocysts was higher in ßME-ßME (181.2 ± 7.4 cells) than CTRL-CTRL (139.0 ± 9.9 cells). Adding ßME to the IVC medium reduced development but increased cryotolerance, whereas adding ßME to the PWC medium improved embryo survival, hatching rates, and total cell numbers.
