Effect of cryopreservation by slow cooling and vitrification on viral contamination of IVF embryos experimentally exposed to bovine viral diarrhea virus and bovine herpesvirus-1.
The objective was to determine the effect of cryopreservation by conventional slow controlled cooling (0.5 degrees C/min) and by vitrification on the presence of bovine viral diarrhea virus (BVDV) and bovine herpesvirus-1 (BHV-1) infectivity associated with frozen-thawed Day 7 bovine embryos. In this study, Day 7 embryos generated by in vitro fertilization (IVF) were exposed in vitro for 1.5h to BVDV (N=393) and BHV-1 (N=242) and subsequently tested before and after cryopreservation for the presence of infectivity. Exposure of embryos to viral agents resulted in 72% of them infected prior to cryopreservation. Stepwise exposure of embryos to cryoprotectants, as well as their removal, substantially reduced the proportion of contaminated embryos (46% vs. 72%, P<0.05). Overall, both freezing methods reduced the percentage of infectious embryos compared with that of embryos similarly exposed to viruses but not cryopreserved (31% vs. 72%, respectively; P<0.001). The percentage of embryos with infectious viruses was not significantly higher after vitrification than after slow cooling (38% vs. 22%). In addition, after cryopreservation, a higher percentage (P<0.002) of embryos exposed to BHV-1 (42%) remained infectious than did embryos exposed to BVDV (24%). In conclusion, cryopreservation reduced the proportion of infected embryos but did not render all of them free from infectious pathogens.
Bielanski
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Animal Diseases Research Institute, Ottawa, Ontario, Canada. bielanskia@inspection.gc.ca
Lalonde
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D000818:Animals; D001755:Blastocyst / Q000821:virology; D002417:Cattle / Q000196:embryology* / Q000821:virology*; D015925:Cryopreservation / Q000379:methods / Q000662:veterinary*; D001908:Diarrhea Viruses, Bovine Viral / Q000302:isolation & purification*; D005260:Female; D005307:Fertilization in Vitro / Q000379:methods / Q000662:veterinary*; D007242:Herpesvirus 1, Bovine / Q000302:isolation & purification*; D008297:Male