Embryo transfer in relation to bovine leukemia virus control and eradication.

Two hundred and seven, zona pellucida-intact bovine embryos were collected from bovine leukemia virus-infected donors, washed, and transferred to uninfected recipients: 111 of these embryos were sired by bovine leukemia virus-infected bulls. Fifty live calves were obtained from the 57 pregnancies resulting from the transfers. None of the recipients or calves developed antibodies to bovine leukemia virus. Nine zona-intact ova, 12 zona-intact morulae and 15 hatched blastocysts, exposed "in vitro" to bovine leukemia virus, washed and then tested for bovine leukemia virus were negative. Twenty-seven, zona-intact embryos and 14 hatched embryos were similarly exposed and washed prior to being transferred in groups to two uninfected recipients: no pregnancies resulted, nor did the recipients develop antibodies to bovine leukemia virus up to 120 days posttransfer. The conclusion from these and other bovine leukemia virus studies is that zona-intact embryos can be transferred from bovine leukemia virus-infected donors, including those bred by bovine leukemia virus-infected bulls, without risk of transmitting bovine leukemia virus, providing that they are properly washed prior to transfer.