REPLICATION OF CYTOPATHIC AND NONCYTOPATHIC BOVINE VIRAL DIARRHEA VIRUS IN ZONA-FREE AND ZONA-INTACT IN VITRO-PRODUCED BOVINE EMBRYOS AND THE EFFECT ON EMBRYO QUALITY

The aim of the present study was to determine whether or not cytopathi c (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 developm ent. Zona pellucida (ZP)-free oocytes, zygotes, 8-cell-stage embryos, morulae, and hatched blastocysts (HE) were incubated for 1 h in 1 mi o f Minimal Essential Medium containing 10(6.00) tissue culture infectio us dose (TCID)(50)/ml NCP BVDV isolate 22146 or 10(6.25) TCID50/ml CP BVDV strain Oregon C24V. At 0, 12, 24, 36, 48, 60, and 72 h postinocul ation (hpi), groups of embryos were collected for virus titration. A s mall 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 m orulae and HE, maximal intracellular virus titers were, respectively, 10(1.47) and 10(2.33) TCID50/100 cells at 48 hpi for the CP biotype an d 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 o n further development of ZP-free morulae. It can be concluded that ZP- free in vitro-produced embryos are permissive to an infection with BVD V, with increasing susceptibility of the embryos in accordance with th eir developmental stage. In contrast to observations in ZP-free in vit ro-produced embryos, no virus replication or signs of embryonic degene ration were detected in ZP-intact in vitro-derived embryos.