The aim of this paper was the presentation of some problems connected with pregnancies located in the uterine horn contralaterally to the corpus luteum (CL) in cows. Contralateral pregnancies occur very rarely (0.2%) and have a lower chance for development than ipsilateral pregnancy. However, owing to the application of the available biotechnic methods it is possible to introduce the embryo in the uterine horn, contralaterally to the CL and to favor their growth to the time of parturition. Such an action was accomplished even in cows with aplasia of one uterine horn. No statistical differences were found in pregnancy rates after the transfer of a second embryo ipsilaterally or contralaterally to the CL to already inseminated cows. However, better conditions for the development of the pregnancy were on the side of the functional CL even when two fetuses were growing, and the ipsilateral transfer of the second embryo to an already mated cows was a more efficient twin induction technique than a contralateral transfer. The maintenance of an early pregnancy in cows is possible using the exogenous progesterone (P), even in cases of the absence of functional CL on ovary. In cows supplemented with P a spontaneous ovulation can take place along with the establishment of a new CL that is able to maintain the pregnancy. At such a time the formation of CL can be induced pharmacologically. Cows with the newly created CL maintained the pregnancy up to mature parturition, even in cases when the fetus was placed contralaterally to such a corpus. Beneficially for maintaining the pregnancy was the presence on the ovary of accessory CL, independently of the supplementation with P. Their presence limited the occurrence of cases of embryo morality and the abortions of fetuses. Pregnancy losses were not observed in females in which the injection of hCG or GnRH induced the establishment of two new luteal structures. The increase of embryonic survival after bilateral nonsurgical embryo transfer is enabled by the stimulation of recipients with low doses of FSH. This treatment causes the presence of few CL on the ovaries at the day of embryo transfer and enables attaining a high percentage of pregnant females. A considerable portion of them carry twins.
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