CLONING BY NUCLEAR TRANSFER IN THE BOVINE SPECIES

A all in vitro cloning technique was developped in which the reconstit uted embryos from the first cycle nuclear transfer (cloning) were used as blastomere donor for the second cycle nuclear transfer (recloning) . Such method permitted to produce 14,5% of morulae and 14,9% of blast ocysts after the first and second cycle of nuclear transfer, respectiv ely. The rates of birth obtained after transfer of such embryos were 2 1,4% et 20,8% for first and second cycle respectively, corresponding t o 6 et 5 calves for 28 et 24 transferred embryos. Unfortunately, gesta tion pathologies and an increase of birth weights were observed. It se ems that the in vitro presence of gametes and/or embryos may be respon sible of an alteration in the control of gene expression.