Replication of Cytopathic and Noncytopathic Bovine Viral Diarrhea Virus in Zona- Free and Zona-lntact In Vitro-Produced Bovine Embryos and the Effect on Embryo Quality1

The aim of the present study was to determine whether or not cytopathic (CP) and noncytopathic (NCP) bovine viral diarrhea virus (BVDV) are able to replicate within in vitro-produced embryos and to investigate whether inoculation of embryos with BVDV affects their normal development. Zona pellucida (ZP)-free oocytes, zygotes, 8-cell-stage embryos, morulae, and hatched blastocysts (HB) were incubated for 1 h in 1 ml of Minimal Essential Medium containing 10(6.00) tissue culture infectious dose (TCID)50/ml NCP BVDV isolate 22,146 or 10(6.25) TCID50/ml CP BVDV strain Oregon C24V. At 0, 12, 24, 36, 48, 60, and 72 h postinoculation (hpi), groups of embryos were collected for virus titration. A small amount of newly produced virus was detected in 8-cell embryos at 60 hpi (10(1.8) TCID50/100 cells), but only for CP BVDV. For ZP-free morulae and HB, maximal intracellular virus titers were, respectively, 10(1.47) and 10(2.33) TCID50/100 cells at 48 hpi for the CP biotype and 10(0.64) and 10(0.84) TCID50/100 cells at 72 hpi for the NCP biotype. Only an infection with CP BVDV had a significant inhibitory effect on further development of ZP-free morulae. It can be concluded that ZP-free in vitro-produced embryos are permissive to an infection with BVDV, with increasing susceptibility of the embryos in accordance with their developmental stage. In contrast to observations in ZP-free in vitro-produced embryos, no virus replication or signs of embryonic degeneration were detected in ZP-intact in vitro-derived embryos.