[The sexual cycle in the bitch: recent insights and impact on therapy and reproduction control].

Present knowledge about the estrous cycle of the bitch has been reviewed from a morphological, endocrinological and clinical point of view. This cycle is truly biphasic, characterized by its slow motion. It includes pregnancy or pseudopregnancy, and lactation. Corpus luteum function and regression as well as endometrial recovery, following endometrial desquamation at about day 100 of the cycle, are finalized at about days 140 to 150. Soon thereafter, subclinical preparations for the next proestrus can be recognized. Prolactin seems to play an important role as a luteotrophic agent, beginning at about day 30 to 35 of the cycle. Inhibition of prolactin secretion can be used to induce abortion, or to inhibit lactation and to shorten the cycle, or to treat clinical anestrus. Late metestrus and subclinical proestrus, i.e. days 120 to 170 of the cycle, is the most suitable period of the cycle to initiate suppression of the cycle, i.e. prevention of the next estrus, by using progestins with the least tendency for side effects.