Proestrus: This is the first stage, lasting about
7–10 days. You may notice swelling of the vulva and light bloody
discharge. Male dogs will be interested, but the female is not yet
ready to mate.
Estrus: Lasting around 5–10 days, this is the fertile
stage when the female accepts males. Discharge may lighten in color,
and this is the time pregnancy can occur if mating happens.
Diestrus: This stage lasts about 60 days, whether or
not the dog is pregnant. If pregnant, this is when embryos develop. If
not, her body will gradually return to normal.
Anestrus: The resting phase between heat cycles,
lasting about 4–6 months. During this time, there are no signs of
reproductive activity, and the body is preparing for the next cycle.
