Doctor of Philosophy (PhD)


School of Animal Science

Document Type



Although superfetation has been reported in cattle and other species, there is considerable skepticism as to its existence due to the lack of clear evidence in these reports. Other explanations such as embryonic diapause or differential growth of twins have been suggested as more accurate descriptions of the cases reported as superfetation. The hypothesis of this study is that if a viable pregnancy can ensure maternal recognition in cattle, an asynchronous embryo can develop in a more chronologically advanced uterine environment. The objective was to produce superfetation by (1) ovulation induction and artificial insemination (AI) of pregnant cows and (2) transfer of 7-day embryos to cows with more advanced pregnancies. An attempt to produce superfetation by induction of ovulation in mated cattle with human chorionic gonadotropin (hCG) followed by AI was unsuccessful. Ovulation was induced in pregnant cows on day 7 but could not be induced >23 days of pregnancy. Subsequently, it was shown that uterine stage bovine embryos (7-day) could develop when transferred to recipients on day 14 of pregnancy, but not on day 28, day 60, or day 90 of pregnancy. Twins (7 days asynchronous) were produced in a recipient that received two 7-day embryos 14-days post-estrus. Although the younger twin was a heifer and her co-twin was a bull, the heifer was not a freemartin. FSH and hCG treatment 7 days prior to embryo transfer (ET) did not increase the rate of superfetation in 14-day or 25-day mated recipients. The nonsurgical ET technique may have caused pregnancy loss in recipients receiving embryos >25 days post-estrus. Two sets of asynchronous twins were produced by transfer of 7-day embryos to 14-day pregnant recipients. An additional experiment was undertaken to determine if asynchronous embryos could develop following maternal recognition in pregnant cows yet prior to invasion of the contralateral uterine horn by the primary conceptus. Asynchronous twins were produced following transfer of 7-day embryos to a 13-day pregnant recipient but not in 19-day pregnant recipients. Asynchronous twin pregnancies (superfetation) were therefore consistently produced in this series of experiments by transfer of embryos to recipients up to 16 days of pregnancy.



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Committee Chair

Robert A. Godke