The bleeding phase in the dog's heat cycle is the most commonly noticed phase by dog owners. Learning more about the heat cycle in female dogs can help dog owners better understand what to expect. When does a dog go in heat and how long is the female dog's heat cycle? In what stages of the dog's heat cycle are female dogs capable of reproducing? What can be done to clean up messes and for how long should male dogs be kept away from female dogs in heat? These are all important questions. Following is information on the female dog's heat cycle by veterinarian Dr. Ivana Crnec.
Age of Onset
Female dogs reach puberty or reproductive maturity around 8 months of age. The exact age depends mainly on the dog’s breed. Smaller dog breeds tend to go into heat earlier (around 4 months of age). On the flip side, large and giant dog breeds become sexually mature later and go into heat at an older age (from 18 months of age to 2 years).
The heat cycle repeats itself every six months (once again this can vary depending on the breed’s size). This means that after reaching maturity, normal and healthy dogs will go into heat twice a year or every six months.
A female dog's heat or estrous cycle consists of 4 stages, proestrus, estrus and diestrus. Each phase is characterized by different physical events and is limited by hormonal changes.
The heat cycle depends on 3 hormones: estrogen which triggers the start of the estrous cycle, luteinizing hormone (LH) which causes ovulation and progesterone which maintains pregnancy.
The Proestrus Stage of Dog's Heat Cycle
The proestrus phase usually lasts for 9 days but it can vary from 3 days to 17 days in length. During this phase the dog’s body prepares itself for the upcoming pregnancy. However, it should be noted that during this phase the female dog does not accept males.
The proestrus is defined by 2 physical, 1 behavioral and 1 hormonal change. The physical changes include swelling of the reproductive tract and the appearance of first neutral and then reddish to brown discharge.This is the bleeding phase in the dog's heat cycle.
The behavioral change suggests the increased nervousness of the dog. The hormonal change is due to the varying levels of the estrogen that first rises and once it reaches its peak starts dropping.
The Estrus Stage of Dog Heat Cycle
The estrus lasts for 9 days but it can range from 3 to 21 days. During estrus the dog's reproductive area appears swollen and soft, while the discharge decreases in both quantity and color (light reddish or pinkish).
Since the estrogen levels are low, the progesterone levels rise. When the progesterone levels are high, the LH levels sharply spike causing ovulation. The female dog becomes receptive to males within 2 to 3 days after the LH peak.
The hormonal changes during the estrus phase of the cycle trigger behavioral changes. For example, female dogs become flirtatious and start poking males with their noses, they push their rear ends into the males’ chests, they play-bow and lift their tails up or to one side (phenomenon called flagging). When the female dog starts showing these signs she is referred to as being in ‘’standing heat’’.
The Diestrus Stage of Dog Heat Cycle
The diestrus ranges in length from 50 to 80 days. This phase occurs regardless of whether the female is pregnant or not. The only difference is that, if the dog is pregnant, the diestrus will be a little bit shorter than it would be if she was not pregnant. During diestrus the dog's uterine walls thicken and certain hormonal changes occur, but there are no visible signs.
During the diestrus phase female dogs may fall into false pregnancies. This is due to the fact that the hormonal system assumes the dog will be pregnant each and every time she comes into heat.
Even when not mated, the dog will still experience the full hormonal effects of pregnancy, with all the associated physical and mental changes. The physical and mental changes include labor signs, milk production, rejecting food, making dens and mothering objects (usually toys).
The Anaestrus Phase of Dog Heat Cycle
As the last phase of the heat cycle, the anestrus is defined as a resting period for the reproductive tract and usually lasts around 150 days. During this period the female dog's body rests and then prepares itself for the next cycle. The anestrus is not marked by visible signs and the sex hormones are at their lowest.
Length of the Bleeding Phase in the Dog's Heat Cycle
The first drop of blood announces the beginning of the bleeding phase in the dog's heat cycle. During the so called bleeding phase, the bloody discharge changes. At first it is light and then it turns darker (reddish-brown).
By the end of the bleeding phase in the dog's heat cycle, the discharge once again becomes lighter (reddish-pink) or even straw in color. The overall length of the bleeding phase is around 10 days.
Should male dogs be kept away during the bleeding phase in the dog's heat cycle? Usually female dogs are not receptive of male dogs during their bleeding phases. However, there are exceptions to the rules and since getting pregnant during bleeding is possible, it is best advised to keep males away during the bleeding phase.
Female dogs are fertile 2 to 3 days after ovulation. This is because after being released from the ovaries the eggs need to spend some time in the uterine tubes and mature. There are tests and diagnostic procedures that can help determining the time during which the female dog is fertile.
Bleeding cycles can be messy especially in larger dogs. The best way to prevent those messes during the bleeding phase in the dog's heat cycle it to use some form of containment. The solutions include using doggy diapers, crating your dog and confining your dog to an area covered with easy-to-clean flooring.
Troublesome Bleeding After a Dog's Heat Cycle
Continuous bleeding after the cycle is an indicator for pyometra. Pyometra is a uterine infection caused by pus-forming bacteria that inhabit the dog's womb. It is the most common life-threatening condition in intact females and it can occur at any age.
Female dogs with signs of pyometra require immediate medical attention. The clinical signs vary, depending on patency (the condition of being open) of the cervix.
In cases of open pyometra, pus or abnormal discharge drains from the womb to the outside. The discharge is yellow-green to pink or red-tinged, thick and odoriferous (giving off a smell). Such discharge may often be recognized by dog owners as it accumulates on the skin or hair under the dog's tail or on bedding and furniture where the dog has recently laid.
Affected dogs can be either febrile (have fever) or hypothermic (having low body temperature). Loss of appetite, increased water intake, increased urination and depression may or may not be present.
In cases of closed pyometra, the discharge accumulates in the womb ultimately causing abdominal distension (expansion of the abdomen). Because the bacterial toxins enter the bloodstream, dogs become ill rapidly. The systemic signs of the disease are same as with open cervix pyometra, but usually they tend to be more severe.
The best way to prevent pyometra is by spaying your female dog. Every intact and unsuccessfully mated female dog after its first cycle is at risk of developing pyometra.
About the Author
Dr. Ivana Crnec is a graduate of the University Sv. Kliment Ohridski’s Faculty of Veterinary Medicine in Bitola, Republic of Macedonia.