Effects of vitrification medium composition on the survival of bovine in vitro produced embryos, following in straw-dilution, in vitro and in vivo following transfer

This study examined the effects of adding a macromolecule, polyvinylpyrroli done (10% PVP) and a sugar (0.3 M trehalose) to vitrification solutions (VS ) containing either one (408 ethylene glycol [EG], two (25% FG + 25% DMSO) or three (20% EG + 20% DMSO + 10% 1,3-butanediol [BD]) permeable cryoprotec tants on the survival and hatching of IVP bovine embryos, following vitrifi cation, warming and in-straw cryoprotectant dilution. Grade 1 and 2 compact morulae and blastocysts were selected on Day 7 (Day 0 = IVF) of culture in SOFaaBSA and equilibrated for 10 min at room temperature in 10% EG. Follow ing exposure, for up to 1 min at 4 degrees C, to one of the above VS (with or without PVP + trehalose), the embryos were loaded into straws and immers ed in liquid nitrogen. Following warming and in-straw cryoprotectant diluti on, the embryos were cultured for 48 h to assess hatching. There was no eff ect of VS on the survival of embryos after 24 h, however fewer compact moru lae than blastocysts survived after 24 h (24% vs. 75%; P < 0.001) or hatche d after 48 h (15% vs. 59%; P < 0.001). When blastocysts only were considere d, an interaction between VS and additional PVP + trehalose was also observ ed (P < 0.01). Hatching was reduced when they were added to 25% EG + 25% DM SO (70% vs. 45%) but was not affected for either 40% EG (44 and 49%) or to 20% EG + 20% DMSO + 10% BD (72 and 72%). Pregnancy rates (Day 90 ultrasound ) of recipients that were transferred either two non-vitrified or two vitri fied (20% EG + 20% DMSO + 10% ED) blastocysts, did not differ (3/6 [50%] an d 11/20 [55%]). However, significantly (P < 0.02) fewer recipients that rec eived compact morulae maintained pregnancy to Day 90 although this was nor affected by vitrification (fresh vs. vitrified; 1/5 [20%] vs. 3/18 [17]). T hese data demonstrate that a. VS comprising three cryoprotectants, rather t han one, enables more embryos to hatch during post-thaw culture and that th e survival, following direct transfer of these vitrified embryos, is not di fferent to non-vitrified embryos. (C) 2000 Elsevier Science B.V. All rights reserved.