To some extent, the experimental design also facilitated the likelihood
of viral transmission to embryo donors and recipientsand its detection because: (1) the embryo donors were exposed to a relatively high titer of virus via two inseminations;
(2) two embryos were transferred into each recipient on many occasions; (3) fresh embryos were transferred; and (4) fresh embryos were tested for thepresence of infectious virus. Nevertheless, in most respects, our experimental approach closely mimicked the usual procedures in ET practice, and recommendations given in
the IETS manual [4,20] and OIE [14] for the production and
transfer of in vivo-produced embryos were followed. Particular attention was paid to washing fertilized and degenerated embryos because it might indicate the
potential effectiveness of the decontamination procedure of embryos selected for ET [20]. However, trypsin treatment was omitted in our washing protocol because this has
not been shown to be consistently effective for the removal of BVDV from embryos [22,23].