Abstract
Abstract
Forty gilts and sows were used to transfer Day 5 embryos into one uterine horn, while Day 7 embryos were transferred into the other horn, of Day 6 nonpregnant recipients (Day 0 = first day of estrus). The survival of the transferred embryos was determined on Day 11 (Expt 1) and Days 60 to 70 (Expt 2). The percentage of Day 5 and 7 embryos surviving the transfer procedures on Day 11 was not different, 42 ± 10 and 43 ± 12, respectively. However, by midgestation (Day 60) more (P < 0.001) fetuses that developed from Day 7 embryos survived than fetuses that developed from Day 5 embryos, 63 ± 8 and 8 ± 7%, respectively. These experiments indicated that the presence of embryos more advanced in development caused the demise of younger embryos sometime between Days 11 and 60 of gestation.
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