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Fetal survival rate after the surgical transfer of two bovine embryos

Summary. Single embryos were bilaterally transferred on Day 7 to the tip of the uterine horn ipsilateral to the corpus luteum and to the tip of the opposite horn, to the tip and contralateral base, base and tip and base and base (20 recipients/group). Ten of the recipients in each group were treated with 1000 i.u. hCG daily from Days 13 to 35 after oestrus. At 42 days, pregnancy rate (N.S.) and fetal survival rate (P < 0·05) were greater when an embryo had been transferred to the tip rather than to the base of the ipsilateral horn, but the twin pregnancy rate was not improved. Treatment with hCG had no effect on these rates but the corpora lutea of treated animals were heavier (P < 0·02).

Unilateral transfers of 2 embryos were made both to the tip of the ipsilateral uterine horn or one to the tip and one to the base (20 recipients/group). The pregnancy rate, fetal survival and twin pregnancy rate in each group were the same, but in the latter one of the embryos had migrated to the other horn in 5/9 animals with twin fetuses. The location of fetuses did not influence their rate of development as determined by fetal measurements.

It is concluded that the tip of the ipsilateral uterine horn is the optimal site for fetal survival and that to ensure a high twin fetal survival one embryo must be in this site.