You likely already know that intact (unspayed) female dogs bleed but may be wondering why do dogs get a period? In reality, dogs do not get a period like women do as their reproductive system works different. 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.
Dogs Get Heat Cycles
Dogs do not get menstrual cycles with a period every month like women do, they get heat cycles instead.
Dogs generally tend to go into heat every 6 to 12 months (depending on breed) and their heat cycle lasts for about three weeks.
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 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. If the dog is pregnant instead, her body gets ready to support the pregnancy.
Cause for Bleeding
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 knwn as serum) noted by dog owners, explains veterinarian Dr. Bruce Christensen.
A dog bleeding during a heat cycle is therefore very different from menstruation, considering that in women the onset of a period is suggestive of a period of infertility, while in female dogs it's a clear indication that they are getting ready to become receptive, and possibly pregnant. In dogs therefore, rather than signaling the conclusion of a cycle, bleeding 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
- Do Dogs Dream? By Stanley Coren
- DVM360, Canine breeding management--vaginal cytology (Proceedings)