A dog’s heat cycle, also known as the estrous cycle, is the period when a female dog can become pregnant. The heat cycle lasts 18-24 days on average and occurs roughly every 6 months once a dog reaches sexual maturity. There are four stages of the heat cycle: proestrus, estrus, diestrus, and anestrus. Understanding the end of the heat cycle, when a dog transitions from estrus to diestrus, is important for dog owners and breeders. The transition marks the end of the fertile period when a dog can get pregnant. Additionally, hormonal and behavioral changes occur as progesterone levels increase and estrogen levels decrease. Being aware of these changes helps owners know what to expect from their dog during this time.
Signs of Proestrus Ending
As the proestrus stage comes to an end, there are some clear signs that a dog’s heat cycle is transitioning to the next phase. According to the Cornell University College of Veterinary Medicine, one of the most noticeable changes is that the bloody discharge lightens in color and reduces in amount as estrogen levels start to decrease. The vulva will also begin regressing in size and appear less swollen as proestrus draws to a close.
The VCA Animal Hospitals also note that vaginal bleeding reduces toward the end of this stage. As proestrus ends, the dark red discharge transitions to a lighter pink or straw color. Owners may also notice less frequent licking of the vulva area as the swollen genitals become less irritated.
Overall, the most distinct signs that proestrus is ending are the lightening of vaginal discharge and shrinking of vulvar swelling. This indicates the dog’s hormones are shifting as the heat cycle progresses to the estrus stage.
Transition to Estrus
As proestrus ends, the discharge stops and the bitch transitions into the estrus phase. This transition period between proestrus and estrus typically lasts around 7-10 days according to Cornell University College of Veterinary Medicine. During this time, estrogen levels increase while progesterone levels remain low. TheExternal vulva begins to appear swollen. The bitch will start expressing more interest in male dogs and may begin flagging, which is when she lifts her tail and exposes herself to males to signal she is ready for breeding.
Behavioral Changes
As estrus begins, the female dog’s behavior will change dramatically as her body prepares for mating. One of the most noticeable changes is that the female will now allow mating with males.
Male dogs will likely begin showing a heightened interest in the female as she enters estrus. They may exhibit mating behaviors like mounting and will be highly motivated to seek out the female in heat. The female will be receptive to the male’s advances and stand to be mounted.
The female dog’s behavior may seem restless or anxious, as she becomes more alert to the presence of males. She may try escaping confinement or roam away from home in search of males. It’s important to keep the female secured during this time if you do not intend to breed her.
In addition to allowing mating, the female dog may exhibit other signs of heat like flagging her tail, swollen vulva, and bloody discharge. Her appetitite may decrease as well. The intense drive to mate only lasts for around 5-10 days before the female will reject male advances as estrus ends.
Optimal Breeding Window
The optimal time to breed a female dog during her heat cycle is usually days 2-5 of estrus, when ovulation occurs. According to the American Kennel Club, “Dogs go through a further maturation phase post ovulation so their optimum fertile period is Days 4 through Day 6” [1]. This fertile window is when you want to allow mating or perform artificial insemination for the best chances of conception.
Typically, ovulation happens about 2 days after the LH hormone surge, which kicks off estrus. This LH surge also prompts the release of eggs from the ovaries. When the eggs are available in the reproductive tract, the female is most fertile [2]. Allowing mating during days 2-5 targets this period of peak fertility.
It’s important to properly identify when estrus begins, as this signals the lead-up to ovulation. Signs of estrus include swelling of the vulva, vaginal discharge, and standing heat (allowing mating). An optimal breeding window occurs a few days into these estrus signs as ovulation approaches.
Changes as Estrus Ends
As a dog’s estrus cycle draws to an end, her body begins going through changes again in preparation for the next cycle. One of the most notable changes is in vaginal discharge. According to the VCA Animal Hospitals, discharge starts to reappear during this stage but it is often more watery and straw-colored compared to the bloody discharge seen earlier in estrus (https://vcahospitals.com/know-your-pet/breeding-for-pet-owners-estrus-and-mating-in-dogs).
The vulva will also continue to decrease in size and swelling as progesterone levels drop and the body transitions out of the estrus phase. According to Cornell University, the vulva that was engorged and swollen during estrus shrinks back down over the course of diestrus as the heat cycle ends (https://www.vet.cornell.edu/departments-centers-and-institutes/riney-canine-health-center/canine-health-information/dog-estrous-cycles). This involution of the vulva is a clear sign estrus is concluding and the heat cycle is nearing its end.
Transition to Diestrus
As estrogen levels decrease and progesterone levels increase, the dog transitions from estrus to diestrus. This phase is characterized by the end of sexual receptivity, discharge stopping again, and the prevention of pregnancy in dogs that did not become pregnant during estrus (Cornell).
During diestrus, discharge stops and the vulva returns to a normal size and appearance. The diestrus phase typically lasts around 60-90 days from the end of estrus/high fertility, though it may last for as little as 60 days or up to 160 days in some dogs (DVM360).
Hormonal Changes
As estrus ends, progesterone levels continue to rise while estrogen levels decrease. According to the Cornell University College of Veterinary Medicine, progesterone levels are low during proestrus and estrus but then rapidly increase during diestrus to prevent further mating and pregnancy. The increase in progesterone inhibits the release of FSH and LH hormones, which prevents follicular development and ovulation. Progesterone levels will remain elevated during diestrus until declining just before the next proestrus phase. According to East Central Veterinarians, diestrus is characterized by low estrogen but high progesterone levels.
According to an article in DVM360, progesterone levels begin rising more quickly during estrus and peak about 20-30 days into diestrus in most dogs. Younger bitches may have a shorter diestrus with lower progesterone levels compared to older bitches. The sustained high progesterone levels prevent any subsequent estrous cycles until diestrus ends and progesterone drops.(Source)
Behavioral Changes
As estrus ends, female dogs will begin refusing mating from males.“Behaviors of Intact Female Dogs in and After Heat.” PetHelpful, 11 Mar. 2023 This is one of the clearest signs that the fertile period has passed. Whereas the female was previously receptive to males, she will now react aggressively or try to avoid them. She is no longer signaling her readiness to mate.
Some females may begin exhibiting nesting behaviors, especially if they have become pregnant during the heat cycle.“Dogs in Heat: Frequently Asked Questions | Four Paws.” Four Paws She may shred paper, fabric or other material and arrange it into a nest. This maternal instinct to prepare a den for the arrival of puppies can sometimes occur even if the dog is not actually pregnant.
Conclusion
The end of a dog’s heat cycle marks an important transition point. As proestrus ends, estrogen levels drop off, stopping the bloody discharge and allowing the female to enter estrus. This estrus period is the optimal time for breeding. However, estrus is short, lasting around 5-10 days. Changes in behavior, vaginal appearance, and hormonal levels all indicate estrus is ending as the dog transitions into diestrus. The non-receptive diestrus phase will last a couple months before the cycle begins again. Carefully monitoring a dog’s behavior and physical changes is crucial for identifying the fertile window. Being aware of the heat cycle phases empowers owners to make informed breeding or spay/neuter decisions. Understanding a dog’s biology leads to better care and outcomes.
