You likely already know that intact (unspayed) female dogs bleed but may be wondering why do dogs get a period? By understanding how a dog's heat cycle works, you can understand why it is wrong to say that "dogs get a period." Here's a brief guide to learn the differences and understand why dogs bleed during their heat cycle.

The Heat Cycle in Female Dogs

Dogs do not get menstrual cycles with a period every month like women do, they get heat cycles instead. Most females dogs have heat cycles twice a year on average, except the Basenji, wolf hybrids, and some Greyhounds, which cycle once yearly.

A female dog's heat cycle, also known as estrous cycle, consists of 4 distinct stages: proestrus, estrus and diestrus. Each phase is characterized by different physical events and is limited by hormonal changes.

When dogs bleed, it's sign that they are in the proestrus stage of the cycle, a stage that lasts for about a week. During this time, male dogs are interested in the female, but the female does not allow them to mount...yet.

Afterward, the blood turns straw colored for another week. It is during this stage, known as the estrus stage, that female dogs are most fertile. During this time, female dogs are receptive to male dogs and will allow mounting.

The third week is when female dogs are finally going out of season and the discharge will stop. Male dogs may still stick around during this stage, but female dogs will no longer allow mounting.

This final stage is known as diestrus, and if the dog was not impregnated during the estrus stage, the body returns to a state of normalcy and prepares itself for the next cycle. The anestrus is not marked by visible signs and the sex hormones are at their lowest. If the dog is pregnant instead, her body gets ready to support the pregnancy.

Did you know? Female dogs may undergo what is known as a "false pregnancy" or "phantom pregnancy" developing several signs of being pregnant, when they are not. Discover more about this phenomenon here: false pregnancies in dogs. 

If Not a Period, Then Why Do Female Dogs Bleed?

If the bleeding intact female dogs show during their heat cycle is not a "period" in the real senses of the word, then what is the cause for the bleeding? 

Dogs bleed at the beginning of their heat cycle and therefore before ovulation. Unlike humans, dogs are not sloughing off their uterine lining (the inner wall of their womb), Instead, dogs tend to reabsorb it rather than getting rid of it.

In female dogs the bleeding instead is triggered by the hormone estrogen. Basically, what happens is that estrogen triggers the blood vessels of the uterus to become highly permeable. 

Through a process known as diapedesis, the red blood vessels will leak and cause the serosanguinous discharge (containing blood and the liquid part of blood known as serum) noted by dog owners, explains veterinarian Dr. Bruce Christensen in an article for DVM360.

Female dogs are expected to be actively bleeding for about about 9 days.

Female dogs are expected to be actively bleeding for about about 9 days.

How Long Do Female Dogs Bleed?

When dogs start to bleed, it is proof that the dog has entered the proestrus phase of the heat cycle. This phase usually lasts for 9 days, but it can vary from 3 days to 17 days in length.

The proestrus phase is signaled by two physical, one behavioral and one hormonal change. The physical changes include swelling of the reproductive tract and the appearance of blood. The blood of a female dog in heat is typically light at first and then it turns darker (reddish-brown).

The behavioral change suggests the increased nervousness of the dog. Male dogs may try to approach, but the female dog typically rejects them.

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The hormonal change is due to the varying levels of the estrogen that first rises, and then, once it reaches its peak, starts dropping.

Female dogs are expected to be actively bleeding for about about 9 days, however, as mentioned, it can be last as little as 3 days or as long as 17 days, explains veterinarian Dr. Ivana. 

The Onset of Fertility

Once the blood decreases in both quantity and color (turning light reddish or pinkish or straw-colored, this indicates that the proestrus phase is over and the dog is entering the estrus stage. 

This is the time when the female dog becomes receptive to males, acting flirty and start poking male dogs with their noses. When the female dog starts showing these signs she is said to be in ‘’standing heat’’ and fertile (capable of getting pregnant).

 Breeders will therefore often consider breeding at this time, which is in general 9 days after the bloody discharge was first detected, however, a compounding factor is when they are faced with dogs with shorter or longer than average proestrus stages.

A dog bleeding during a heat cycle is therefore very different from a woman's period. One of the main differing factors between menstruation in women and the bleeding in female dogs is that it signals the onset of fertility, while in women, the onset of a period is suggestive of a period of infertility.

In female intact dogs therefore, the bleeding is a clear indication that they are getting ready to become fertile, and possibly pregnant. 

 It can be therefore concluded that, rather than signaling the conclusion of a cycle, as it happens with women, bleeding in dogs marks the onset of fertility.

"In human females vaginal bleeding during menstruation indicates a period of infertility, but in dogs the indication that a female is about to go into heat starts with a bloody discharge that then turns clear ."~Stanley Coren

Managing the Bleeding 

Bleeding cycles can be messy, especially in larger dogs. While women use pads for managing the bleeding during a period, there are also some forms of containment when it comes to female dog "periods."

Doggy diapers are available nowadays in various forms. There are disposable diapers for dogs that can be used and tossed away, and there are washable, and therefore re-usable. 

If your female dog in heat doesn't tolerate wearing diapers, then it helps crating your dog or confining your dog to an area covered with easy-to-clean flooring.

Dispelling a Myth

Often, people assume that the amount of bleeding seen during the dog's proestrus phase is an indicator of fertility. This though turns out being untrue. 

Dogs with minimal bleeding are not less fertile compared to dogs bleeding more, and nothing needs to be done to give them a “stronger” heat, points out Dr. Margaret V. Root Kustritz, a veterinarian specializing in canine reproduction and author of the book: "The Dog Breeder's Guide to Successful Breeding and Health Management."

Signs of Trouble

If your dog in heat stopped bleeding, and then started again once the heat cycle is over, this can be indicative of pyometra. 

The term pyometra indicates a life-threatening uterine infection. It may occur at any time in the days, weeks, or months after an estrous cycle and requires immediate veterinary attention. You can read more about this here: help, my dog in heat stopped bleeding and started again.

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