Effect of chilling on the development of in vitro produced bovine embryos at various cleavage stages

Abstract

Purpose: Bovine embryos and zygotes are known to be sensitive to "temperature shock" when cooled to temperatures near 0°C. The effect of chilling on in vitro derived embryos at various cleavage stages was investigated. Methods: Cumulus-oocyte-complexes (COCs) were matured in IVM medium with serum. Presumptive zygotes were cultured in serum free in vitro culture (IVC) medium. Embryos were used as chilled or control samples at the 2-cell, 4-cell, 8-cell, morula, and blastocyst stages. Embryos in 0.2 mL PBS in plastic straws were cooled rapidly in ethanol baths at 0°C for 30 min. Embryo viability was assessed by in vitro development. Results: The percentage of control embryos that hatched as blastocysts increased the later stage at which they were selected. Relative proportion of embryos increased from 28% to 48% to 68% when chilled at the 8-cell, morula or blastocyst stages. Conclusions: IVF-produced embryos are differentially susceptible to cooling injury. Cell counts made of those blastocysts formed from chilled embryos indicated subtle effects of chilling. © 2006 Springer Science+Business Media, Inc.