Preovulatory progesterone secretion terminates the duration of reproductive behavior during heat in the bitch.

To evaluate the role of preovulatory progesterone on canine sexual behavior and the course of proestrus and estrus, seven bitches in spontaneous cycles were treated with aglepristone for temporary elimination of progesterone action. Aglepristone was administered at the dose 10 mg/kg b.m., two times 24 hours apart, beginning in early proestrus when progesterone concen- tration was ⟨0.5 ng/ml. Seven untreated bitches served as a control group. Reproductive sexual behavior (standing behavior, display vulva, tail deviation) was evaluated according to behavioral score. Cytologic, clinical and vaginoscopic examinations and progesterone measurements were used for the determination of proestrus and estrus and estimation of ovulation time. Although, a similar pattern and magnitude of sexual behavior were observed in both groups, the duration of a total reproductive behavior was significantly extended (28.71 ± 2.06 vs 17.00 ± 2.45, p ⟨0.05) in experimental group; similarly, the length of cytologic estrus (23.86 ± 3.02 vs 11.14 ± 2.41, p ⟨0.05) was prolonged in treated bitches. In contrast, ovulation rate, duration of proestrus did not differ between the groups (p >0.05). We conclude, that during the canine estrus cycle the preovulatory progesterone terminates the duration of reproductive behavior and cytologic estrus.