Transuterine embryo migration in recipient cattle.

摘要

Heifers receiving 1 or 2 in vitro-produced embryos were studied to determine (1) the incidence of transuterine migration, (2) the timing of migration and (3) the random or systematic occurrence of the event. In 4 experiments, 436 heifers received embryos and 218 of these were pregnant at necroscopy on day 14, 18, 26 or 60 of pregnancy. 20% (43/218) of the heifers had embryos that had migrated. The frequency of migration was higher (P<0.001) in twin (30/68) than in single (13/150) embryo transfers of pregnant recipients (44 vs. 9%), and in contralateral (9/15) than in ipsilateral (33/170) transfers (60 vs. 19%). Among the heifers that received embryos by ipsilateral transfer, the migration rate was similar to that in heifers pregnant with a singleton after the transfer of either 1 (2/48) or 2 (4/60) embryos (4 vs. 7%). The migration rate was highest at day 26 (12/37) in heifers receiving twin embryos by ipsilateral transfer but was similar at all other stages of pregnancy (15/111, 32 vs. 14%; P<0.01). Migration was first observed by day 14, and further migration probably occurred over the next 12 days or was associated with a higher survival rate from day 14 to day 26. The low migration rate at day 60 indicated that migration by day 26 was associated with increased embryo or fetal death by day 60. The results indicated that embryo migration was probably independent for each of a pair of surviving embryos. It is concluded that embryo migration is embryo-dependent in cattle, and that this capability is dormant unless >1 embryo is present in a uterine horn or the embryos are transferred to the contralateral uterine horn.