Bovine Early Pregnancy Factor in Recipient Serum with Embryo Transfer on the Day More Than 5 Days Different from the Estrus Cycle of Donor

Abstract

Bovine early pregnancy factor (EPF) has been detected in the recipient serum after embryo transfer which was performed on day 7 to 8 after estrus. However, there have been no reports of the detection of EPF in the recipient serum with embryo transfer on the day more than 3 days different from the estrous cycle of the donor. The aim of this study was to determine if EPF is detectable from serum of Holstein cow recipients with embryo transfer on day 12 to 16 after estrus which was 5 to 9 days earlier than that of the donor. Embryos were collected nonsurgically from superovulated Holstein cows on day 7 to 8 after artificial insemination (AI). The embryos were transferred nonsurgically to seven recipients on day 12 to 16 after estrus. Blood samples of the recipients were collected on day 0 (the day of embryo transfer) to 15. EPF activity was assayed by the rosette inhibition test. A rosette inhibition titer (RIT) above 4 was regarded as indicating positive EPF activity. EPF activity was positive in the serum of seven recipients on day 2 to 3 after embryo transfer. Subsequently, six recipients out of seven remained positive for 2 to 3 days. As for the other recipient, positive EPF activity was maintained until day 15 and then a female calf was delivered on day 268 after embryo transfer. These results provided evidence that EPF was detected in the serum of recipients of transferred embryos and was indicative of embryonic life (or existence of the embryo) on even day 12 to 16 after estrus, which was 5 to 9 days earlier than that of the donor