EFFECTS OF TIME OF DEOXYRIBONUCLEIC-ACID MICROINJECTION ON GENE DETECTION AND IN-VITRO DEVELOPMENT OF BOVINE EMBRYOS

In vivo fertilized embryos were surgically collected from superovulate d dairy cows to evaluate microinjection on embryo development and util ized the polymerase chain reaction technique for selection of transgen ic embryos. Seventy-two percent of the embryos with visible pronuclei or nuclei were microinjected with DNA, and the remaining 28% served as uninjected controls. All embryos were cocultured with bovine oviducta l epithelial cells. Mean final development scores of embryos within th e same initial cell stage at collection were unaffected by microinject ion. After 144 h of culture, 45% of the microinjected embryos develope d to the morula or blastocyst stage. The transgene was detected in 50, 10, and 9% of demimorulae from embryos microinjected at the 1-, 2-, a nd 4-cell stages. Frequency of transgene detection was higher in morul ae from 1-cell embryos than in morulae from 2- and 4-cell embryos. Use of in vitro coculture, embryo bisection, and polymerase chain reactio n technique facilitated selection of bovine embryos that carried the t ransgene.