The Occurrence of an Antigen Associated with Pregnancy in the Ewe

Precipitating antisera raised in calves against whole 14–16 day ovine conceptuses were rendered specific to antigens associated with ovine pregnancy by absorption with liver and kidney tissue from nonpregnant ewes. Using agar gel double diffusion, the pregnancy associated antigen was detected in 100% of samples of trophoblast tissue (n=30) and uterine tissue (n=31) and 94% of samples of uterine flushings (n=89) from pregnant ewes. Antigen was also detected in 27% of samples of uterine tissue (n=148), but not in uterine flushings (n=128) from nonpregnant ewes. The incidence of detection of antigen in uterine tissue from nonpregnant ewes was higher in ewes which were exhibiting cyclic ovarian activity (43%, n=83) than in nonpregnant ewes which were anestrous or prepubertal (7%, n=60). The results suggest that the incidence of detection of antigen in uterine tissue varies depending on the reproductive state of the animal.