The Dog Heat Cycle

The reproductive dog heat cycle of the bitch is broken up into 4 phases (Pro-estrus, Estrus, Met-estrus and Di-estrus), day 1 of Pro-estrus being the first day of vaginal bleeding ie the day she visibly comes “on heat”.

Stage 1 of the Dog Heat Cycle

Pro-estrus:  Eggs develop in follicles on the ovaries and produce estrogen.

Duration:  A few days to 3 weeks (typically 9 days)

Starts on first day of bleeding.  Be warned however – about half of all bitches do NOT show obvious signs of bleeding!  You can check for sure by either using a teaser dog, and/or vaginal cytology tests (these can be done successfully and cheaply at home).  Another trick is to line her bed with a white sheet so any bleeding is more likely to be seen.  Also, getting her out of the house on a solid walk every day will expose her to the smells of other dogs and help induce her dog heat cycle.

A bitch’s heat is initiated by developing egg cells (“follicles”) on her ovaries which produce increasing amounts of estrogen as they mature.  Her vulva will be soft and swollen, and (may) show a bloody discharge.

The bitch will be very attractive to male dogs but (normally) not allow them to mate. She will flirt, snap, paw, sit down, evade and circle with males but will (normally) not stand still and cooperate when they attempt to mount her.

Allowing this flirtation stimulates production of hormones and eggs in the bitch, resulting in larger litters.

Once the egg follicles on the ovary are mature, their production of estrogen starts to wane.  This triggers the pituitary gland of the brain to produce a hormone called Luteinizing Hormone.

Stage 2 of the Dog Heat Cycle:

Estrus: The follicles release their eggs into the uterus and produce progesterone.

Duration:  A few days to 3 weeks (typically 9 days)

The start of Estrus is signified by a surge in LH that causes the release of immature eggs from the ripe ovarian follicles.

It takes about 2 more days for these eggs to be mature enough for fertilisation, and once ready, they only live another one to three days.   Ovulation occurs 2 days post the LH surge. In the bitch the ova are not mature and capable of being fertilized until an additional 2 days have passed. The mature ova live another 1 to 3 days. Counting the LH surge as day 0, the bold bitch’s peak fertile period is days 4, 5 and 6 post the LH surge.

Missing the fertile period is the biggest cause of small or missed litters.  Learn how to pinpoint your bitches’ most fertile period here.

Behavior during Estrus

Day 1 of Estrus signifies a dramatic shift in the attitude of the bitch.  She basically becomes a little hussy!  During pro-estrus, though very attractive to male breeding dogs, she will resist their advances.  As soon as estrus commences however, she will suddenly start to stand for those she accepts as sexual partners.

Her vulvar will not look as swollen and the discharge, if any, will go from the thick and bloody pro-estrus type to generally less copious pink, brown or straw-colored.

Stage 3 of the Dog Heat Cycle:

Di-estrus:  The Heat is Over

Duration:  typically 2 months

Within a few days following her ripe eggs either dying of old age or being fertilized, the bitch will enter Di-estrus.  Essentially the “heat” is now over and she is either pregnant or she isn’t. Interestingly, her body will go through the same hormonal changes during Di-estrus whether she conceives or not.

The first day of Di-estrus is marked by a dramatic change in the appearance of the cells of her vagina, readily apparent under the home microscope.

Stage 4 of the Dog Heat Cycle:

An-estrus:  Resting Time

Following Di-estrus her reproductive system will take a bit of R and R to recover and prepare for the next cycle.  This period can be as short as 2 months in small breeds or over a year in large ones.

Summary of the Breeding Dogs Heat Cycle

PhaseUsual LengthEvents      



Proestrus5-7 days




Follicles start to develop on ovary.


Uterus lining forms.

Bitch not receptive to male.

May be bloody vaginal secretions.


Estrus4-13 daysOvarian follicles mature, producing estrogen.


Typically less blood in vaginal secretions.

Bitch becomes receptive to mating.

Vulva may be swollen, pink.

Ovulation occurs a few days before estrus ends.


Diestrus7-10 daysFollicles become Corpus luteums and produce progesterone (may be a little bleeding again due to waning estrogen) to support pregnancy.


If they persist without pregnancy a false pregnancy may ensue (common in dogs).


Anestrus3 – 17 mthRest period.



Return from Dog Heat Cycle to Reproductive Dog Breeding Cycle