[Timing of transplantation and success of pregnancy in mammals].

In domestic mammals, the optimum time for embryo transfer greatly depends upon the species and its embryo chronology development and the technique used. Three different models (rabbit, pig, bovine) have been studied to set up the importance of cycle synchrony between donor and recipient. In the rabbit, the best survival rates were obtained after tubal transfer to highly synchronous recipients even for frozen or cultured embryos. In the pig, there was no survival difference after embryo transfer on D2 (oviduct) or D6 (uterus) and an asynchrony up to 24 h was possible. In the bovine, embryo transfer is usually performed at the blastocyst stage directly into the uterus. A retrospective study over 2,000 recipients indicates that the highest pregnancy rates were obtained when the recipient was in heat 12 to 24 h before the donor.