Effects of antibodies to progesterone on reproduction of ewes

Two experiments were conducted to determine the effects of immunization of ewes with progesterone-11alpha hemisuccinate coupled to bovine serum albumin (P-BSA) on estrous cycles, serum progesterone and fertility. In experiment I, ewes were immunized during the first estrous cycle in September and observed through January. Immunization against progesterone increased (P<.01) the proportion of estrous cycles of abnormal length. Two general patterns were evident in the ten ewes which were immunized against progesterone: 4 continued to show cyclic patterns of estrous activity throughout the experimental period and 6 entered periods of anestrus characterized by presence of corpora lutea. Apparent, aberrant, estrous activity and shortened luteal phases were also observed in ewes which were immunized against progesterone. In experiment II, immunization against progesterone caused serum progesterone concentrations to be 4 to 8 times higher (P<.01) than ewes which were immunized against bovine serum albumin. Fertility was reduced (P<.01) by immunization with P-BSA. In experiment II, immunization against progesterone shortened (P<.01) the second estrous cycle post-immunization, and at day 13 of the third cycle corpora lutea in P-BSA-immunized ewes were regressing and were lighter (P<.05) than in ewes which were immunized with bovine serum albumin.