Maltese dogs with ribbons in their hair.
Maltese dogs with ribbons in their hair. Photography ©Cynoclub | Thinkstock.

Do Dogs Have Periods?

Do dogs have periods? Well, a dog's estrous cycle is different from the human menstrual cycle — here's how.
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Questions like “Do dogs have belly buttons?” and “Do dogs have periods?” tend to arise from anthropocentrism, the notion that the way humans experience the world is the only way that matters. The first of these questions presumes that, because humans have belly buttons, surely it’s unusual or remarkable that dogs do not.

In fact, humans are the outliers; it is we who are unusual in the grand scheme. “Do dogs have periods?” is a similar question. Among the species that constitute the animal kingdom, only female primates — ranging from the lemur to the human to the gorilla— have periods in the way we generally understand the term.

Menstrual cycle vs. estrous cycle

A female dog with a pink ribbon.
Do dogs have periods? Photography by Claudio alexandre Cologni/Thinkstock.

So, do dogs have periods? While mammals of all sorts — including dogs and humans — share the same basic reproductive organs, the ways those organs function is not similar. Human women go through a menstrual cycle, a process of preparation for egg fertilization that lasts an average of 28 days. Female dogs, on the other hand, go through an estrous cycle, similar in purpose, but different in execution, which lasts an average of 180 days.

One reason we ask, “Do female dogs have periods?” is that bloody vaginal discharge is present in both the menstrual cycle and the estrous cycle. In humans, the uterus builds up nutrients for the anticipated growth of a fetus. When an egg goes unfertilized, that material gets secreted from the body. In dogs, when an egg is unfertilized, that nutrient-rich material is absorbed by the body over an extended period of time. The bloody discharge that emerges from female dogs originates in the vagina, not the uterus, and serves a different function. Rather than marking the conclusion of a cycle, in dogs, it signals the onset of fertility.

The estrous cycle in dogs

So, when we’re asking, “Do dogs have periods?” dog menstruation is a misnomer, since dogs do not menstruate. The estrous cycle in dogs consists of four major phases: proestrus, estrus, diestrus and anestrus. A dog’s vagina discharges blood and other fluids during the first two of these phases, most heavily during proestrus. When we say a female dog is in heat, this constitutes the first two phases, proestrus and estrus.

During proestrus, which can last from three to 17 days, a female dog’s body produces large amounts of estrogen. In dogs, this is accompanied by the start of bloody vaginal discharge, which is dark red to begin with, and caused in part by excessive hormone and pheromone production. Dogs also urinate much more frequently during proestrus. The hormones and pheromones in the blood and urine attract potential mates over large distances.

Estrus is the shortest part of the estrous cycle, lasting from four to seven days. This is typically when a dog is primed for mating and fertilization. During estrus, bleeding tends to continue, though it may slow and take on a lighter tint. Discharge in estrus can range from a lighter shade of red to pink to straw-colored. In this phase, a dog may sleep more, be less inclined to play, and begin building a nest in anticipation of pregnancy.

At the start of the third phase, diestrus, the bloody discharge ceases, whether the dog’s egg has been fertilized or not. Diestrus lasts approximately 65 days, about the same span of time that marks a dog’s pregnancy. If the egg is not fertilized, diestrus is the phase during which the nutrients that have accumulated to nourish the anticipated litter of puppies are reabsorbed by the body. The final phase of a dog’s estrous cycle is anestrus, and for this two-to-three month span, the dog is sexually and hormonally inactive.

Dogs do not experience menopause, either

When we ask, “Do dogs have periods?” we might also wonder, “Do dogs experience menopause?” Because the estrous cycle is so drawn out, female dogs tend to go into heat an average of two times per year. Depending on the size and breed of the dog, the capacity to breed can begin as early as six months of age, or as late as 24 months of age. Given that disparity, the length of an estrous cycle is also size- and breed-specific. Some small dog breeds may go through their reproductive cycle up to three times a year, while some very large dog breeds may complete a full cycle only once per year. Yet another difference between human and canine reproduction is that dogs remain capable of breeding well into seniority, and do not go through menopause.

Spay and neuter your dogs!

There is a bit of folk wisdom that is worth dispelling before we conclude. It is thought that a dog’s long-term health is improved if she is allowed to go into heat once before being spayed. Much like, “Don’t cross your eyes or they’ll stay that way,” this is simply untrue. You can safely spay and neuter dogs starting at six to eight weeks of age thanks to modern veterinary practices.

The benefits of spaying your female dogs are many. Spaying your female dog reduces the chances that she will develop breast, ovarian and uterine cancers later in life. It prevents her from developing a deadly bacterial uterine infection called pyometra, which any unspayed female dog can contract at any age, but the risk increases the older she gets. Get your dogs spayed and neutered! It’s better for everyone!

Thumbnail: Photography ©Cynoclub | Thinkstock. 

This article was originally published in 2014.

Learn more about dog health and care on Dogster.com:

14 thoughts on “Do Dogs Have Periods?”

  1. Concerned Dog Owner

    Giant breed dogs have a dramatically increased risk of osteosarcoma (bone cancer) when spayed too early (as well as other risks like a higher instance of hip dysplasia) . Too early is specified as before 18 months, though it is usually better to wait until 2 years of age to be safe. This kind of blanket misinformation on spaying dogs early (especially at 6-8 weeks which is beyond irresponsible and most reputable Vets will absolutely refuse to spay a dog before 6 months of age) is damaging to the people who need to know it the most – those who are searching here for reliable and truthful information. This article needs to be updated to include the risks of spaying early – of which there are MANY – for ALL breeds. Stop plugging your agenda and tell the actual truth.

    1. Thanks for adding more info, sir/ma’am! I’m a first-time dog owner wondering about dog period. She recently got her period and she’s still less than a year old. We haven’t spayed her yet, but we will.

  2. Wow, this is amazing, covering each and every aspect of what has been worrying me for up-to six days now with my Maltese.
    Have learned so much and even got a thought of spraying her.
    Thank you so much

  3. The end of this article about is bulls##t. Check out Dr Becker: The truth about spaying and neutering, on You Tube.

  4. Thank you kindly for your straight forward explanation of the cycle of the dog and what all happens. Much much appreciated!

  5. When I got my Yorkie about 9 years ago, I had no. Idea staying was important. I saw it as an unnecessary surgery and the vets never said anything about it.

    My one Yorkie got open pyometra at just a few years old, and had to have an emergency operation to remove her uterus.

    And my other Yorkie died (at 9yrs old) last Sept, of mammary cancer. The vet gave her a couple of months to live. She started having less energy and getting wore out faster, and within 2 months she was gone.

    Spaying is very important. I just wish I knew before my babies suffered.

  6. I for one think this article was very well written

    No one like to talk about animal periods in detail, but the author did a great service by writting this edifying piece

    thanks again

  7. This article was quite a haughty read. I clicked this link in my search for more information about the subject and the arrogant manner it was written in made it an unpleasant read. The information was somewhat useful but not enough for the author to take such a presumptious stance on the manner.

    1. This is so funny. Do you read news articles and go “Wow, I can’t believe this information was presented in such an arrogant manner.” Do you read magazine articles and get angry that information is being presented to you as though the magazine is an authoritative source. I love it.

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