Abstract:
The feasibility of embryo chilling and freezing in the pig was studied. Pig embryos at day 7.0, morula, early blastocyst, blastocyst, expanded blastocyst were collected from PMSG/HCG (400:200 iu) stimulated gilts. Four experiments were conducted : Experiment I : Embryos at different stages (n = 48) were cooled to 4 C in TCM 199 2.5 Hepes + 10% DMSO for 1, 6, 12 and 24 hrs. After culture for 24 hrs, no embryos can develop. Experiment II : Embryos at blastocyst and expanded blastocyst (n = 69) were slowly frozen to -196 C by using the rate of 3 C/min. from -7 C to -30 C in TCM 199 2.5 Hepes supplemented with 1.5 M glycerol or 1.5 M DMSO or 1.5 M ethylene glycol. After thawing, the average normality rate was 47.8% (33/69) which was not significantly higher (P>0.05) in ethylene glycol group, 54.3% (13/24) compared to 44% (11/25) in glycerol and 45% (9/20) in DMSO groups. Experiment III : Embryos at blastocyst and expanded blastocyst (n = 102) were frozen by vitrification technique. The embryos were exposed to 25% VS3a (6.58 M glycerol + 6% BSA) for 20 min., 65% VS3a for 1 min. and 100% VS3a for 45 sec., then loaded into 0.25 ml plastic straw with 100% VS3a. The straws were directly plunged into liquid nitrogen (-196 C). The average normality rate of the embryos was 59.8% (61/102), small (100300 micro) sizes were 48.6% (17/35), 65.6% (21/32) and 65.7% (23/35, respectively. Experiment IV: Embryos were exposed to cytochalasin-B with the concentrations of 5, 7.5 and 10 microgram/ml for 30 min. before vitrification as Exp III, compared to control without exposing to cytochalasin-B. The results revealed higher survival in cytochalasin-B groups than in the control, 60% (50/84) vs 46.4% (13/28) (P<0.05). The survival rates in 5, 7.5 10 microgram/ml were 46.4% (13/28), 65.4% (17/26) and 66.7% (20/30), respectively. We concluded from these studies that pig embryos can be frozen by a conventional slow freezing or vitrificantion technique. An exposure of cytochalasin-B increases the survival rate of pig embryos after thawing.