EMBRYO TRANSFER IN THE SHEEP: THE SIGNIFICANCE OF SYNCHRONIZING OESTRUS IN THE DONOR AND RECIPIENT ANIMAL

Abstract

Morulae and blastocysts obtained from ewes 5,7 and 9 days after estrus were transferred to 120 recipients whose estrous cycles were either synchronized or[plus or minus] 2 or 3 days out of phase relative to the onset of estrus in the donors. When synchronization was exact 75% of all recipients became pregnant. A high proportion of pregnancies were, in general, also obtained where the onset of estrus in the recipient differed from that of the donor by [plus or minus] 2 days. With a difference of [plus or minus] 3 days, however, only 8% of ewes became pregnant. The survival of 5-day morulae transferred to 7-day recipients was lower than when 9-day blastocysts were transferred to 11-day recipients. The results are discussed with reference to possible factors associated with early embryonic mortality.