The Estrous (Heat) Cycle
Depending on the breed of your dog, the first heat cycle usually begins at 6 months, with the smaller dog breeds getting into heat earlier than the larger dog breeds. Once the heat cycle has started, you can expect it to occur every 6 months or thereabouts and continue until old age.
Known as proestrus, the first phase usually lasts for 9 days or longer. This is the time when her body is preparing for a possible pregnancy. Some of the obvious signs are the swollen vulva and bloody discharge. At this point, she may be in heat but she will not be receptive to male advancements, at least, not just yet.
It is in the second phase known as estrus when your dog begins to show interest in mating. Her vaginal bloody discharge is reduced or may even stop. You’d also see your dog licks her genital organ frequently and will urinate more as a sign of territorial marking.
Plus, she’d position her tail on the side (tail flagging) as a way of letting a male dog know of her willingness for mating. The estrus phase lasts for an average of 9 days.
The third phase, the diestrus phase, comes after her fertile days and usually lasts for 2 months. At this point, her estrogen level declines while the progesterone level increases 3 to 4 weeks at the start of the diestrus phase and then declines by the end of this phase.
If the mating is successful, expect her to deliver her pups in about 63 days.
The fourth phase is the anestrus which is known as the recovery period. This is the time when the ovaries are inactive and the uterus recovers for another heat cycle and possible pregnancy, regardless of age. This phase normally lasts for 4 months.
How Long Is Your Dog In Heat?
On average, it lasts for 21 days, that is from the start of the proestrus until the end of the estrus phase. The estrus phase is also referred to as standing heat because that is the time when your female dog is willing to mate and stand up for successful copulation.
To determine if she is no longer in heat, refusal to stand up for copulation is one of the signs. If you want to be absolutely certain that she is not in heat anymore, you may opt for a vaginal cytology exam.