EMBRYONIC SURVIVAL IN THE UTERUS OF EWES INSEMINATED AT THE UTEROTUBAL JUNCTION ON DAY 32 POST-PARTUM

Experiments were conducted to determine 1) if pregnancy initiated on D ay 32 post partum would be maintained until lambing, 2) if there is a difference in the ability of the previously gravid or nongravid uterin e horn to maintain pregnancy, and 3) if season has an effect on embryo loss. Estrus was induced in ewes on Day 32 post partum. At estrus, ew es were inseminated surgically at the uterotubal junction and assigned to the following groups: 1) inseminated at estrus and laparotomized o n Day 3 to collect embryos for determination of fertilization rate (C) , 2) inseminated in the previously gravid uterine horn (PG), 3) insemi nated in the previously nongravid uterine horn (NG), and 4) inseminate d when both horns were previously gravid (BG). Ewes pregnant in the PG , NG and BG groups were allowed to lamb. Conception rate in Group C at embryo collection was 70%. Embryo loss, based on concentrations of pr ogesterone at Day 18 post insemination, was 43, 19 and 18% in the BG, NG and PG group, respectively. The high embryo loss in Group BG occurr ed only during the breeding season. Only 24% of the ewes that had been inseminated lambed. This was due to the prepartum loss of embryos and fetuses (47, 48 and 33% in Group BG, NG and PG, respectively. In conc lusion, the detrimental effects of the uterus on embryo survival was e vident within 18 d post insemination in Group BG (breeding season), an d embryo loss prior to lambing was high in all the treatment groups (b oth seasons).