Twin induction by transfer of a second embryo ipsilateral or contralateralto the corpus luteum in mated cows

The purpose of this work was to compare the effect of the site of transfer (ipsilateral or contralateral to the corpus luteum) of a second embryo to a lready mated cows on pregnancy and twinning rate. Thirty two frozen-thawed embryos were transferred ipsilateral to the corpus luteum of recipient cows and twenty eight were transferred contralaterally. On the ipsilateral group 21 cows became pregnant after first service (65.6% ), while 21 out of 28 recipients were diagnosed as pregnant in the contrala teral group (75%). No significant differences were observed between both gr oups. Twin pregnancy rate at 60 and 90 days after service was 57.1 and 45% of pre gnant recipients for the ipsilateral group and 14.3 and 4.8% for the contra lateral group. Significant differences (P < 0.05) were observed between gro ups at both times. Although embryos transferred to the ipsilateral horn have higher probabilit ies to survive when the native embryos are reabsorbed in comparison with th e ones transferred to the contralateral hem, we did not observe differences on the pregnancy rate of both groups after first service. The difference w e observed in the number of twin pregnancies between groups was higher than that described in the literature. These results confirm the fact that the existence of 2 embryos in one uterine horn does not increase the embryo or foetal mortality rate. According to our findings we can conclude that the transfer of a second emb ryo to the ipsilateral uterine horn of already mated cows is a better twin induction technique than contralateral transfers.