Abstract   

The study was aimed at developing a freezing protocol for in vitro produced bovine blastocysts using different concentrations of egg yolk (EY) in the freezing medium In experiment I, the survival rate of embryos in the medium C (72%) containing 20% EY was significantly higher (p <0.01) than in medium-A (34 6%) (no contents of EY and polyvinylpyrrolidone (PVP) There was no difference between media C and B (60 7%) (containing 5% PVP) and also between media B and A This indicate that egg yolk contributed to protection of the blastocyst at this stage In experiment II Post-tha survival rates were 14/29 (48 2%) 27/38 (71.1%), 18/25 (72.0%), 13/34 (38.2%) of 5, 10, 20 and 30% EY respectively. Survival rates in EY 10 and 20% were significantly higher (p <0.01) than that of 30%. There was no difference (p>0.01) between 5, 10 and 20% EY, neither between 5 and 30% EY. With regard to the hatching, the 5, 10, 20 and 30% EY resulted in 4/14(28.6%), 19/27(70.4%), 11/18 (61.1%) and 4/13 (30.8%) respectively. Both 10 and 20% EY were significantly higher (p<0.0l) than 5 and 30%. These results indicated that use of 10 or 20% egg yolk in freezing media resulted in an optimal post-thaw survival and hatching of bovine blastocysts.