The canine estrous cycle, from proestrus to anestrus
Four phases, one long non-seasonal cycle: what defines each stage in the bitch.
The bitch is monoestrous and non-seasonal, cycling on average every 6 to 8 months. Each cycle consists of proestrus, estrus, diestrus and anestrus, each with characteristic behavioral, cytological and endocrine signatures.
- Proestrus lasts on average 9 days and is marked by serosanguinous discharge and rising estradiol.
- Estrus lasts on average 9 days and is defined by acceptance of the male and the LH surge.
- Diestrus lasts approximately 60–65 days regardless of pregnancy — the origin of pseudopregnancy.
- Anestrus lasts 3–5 months on average and is required for full endometrial recovery.
Behavioral markers
Proestrus females attract but reject males; estrus females accept mating and often present flagging behavior; diestrus females reject mating again. These behaviors are not perfectly synchronous with the endocrine cycle and should never be the sole timing tool.
Cytological markers
Vaginal cytology shifts from parabasal and intermediate cells during proestrus toward >80–90% cornified superficial cells during estrus, then abruptly returns to intermediate cells at the diestrus shift — a useful retrospective marker.
Clinical use
Cycle staging is best done combining behavior, cytology, and quantitative progesterone. Interpretation and any clinical decision must be made by a licensed veterinarian.
References
- Concannon PW. Reproductive cycles of the domestic bitch. Anim Reprod Sci. 2011.
- Johnston SD, Root Kustritz MV, Olson PS. Canine and feline theriogenology. Saunders.
Educational information only. Does not replace veterinary consultation. No diagnosis. No prescriptions. No emergency advice.