Vagina Museum
Being a museum dedicated to vaginas, vulvas and the gynaecological anatomy, we run up against a lot of myths about the world's most misunderstood body parts. Heck, we even dedicated an entire exhibition to the topic.
One myth we encounter fairly frequently is that dogs have periods. Today, we're going to address that...
Kit Rhett Aultman
@Kay @vagina_museum Right. They do, but it is not menstruation and it is not from the same part of the cycle as it would be in menstruation either.
Kay :heart_bi: :tinoflag:
@vagina_museum a friend's female dog had cyclical bleeding from her vagina. I knew because I saw the blood and asked if the dog was OK. Hard not to believe my own eyes.
Vagina Museum
Having a menstrual cycle is very rare in nature. A period is a phase in the ovarian cycle where the endometrium - the lining of the uterus - is shed. It will then regenerate each cycle, because for whatever reason, embryos only implant in fresh endometrium.
Only a handful of animals shed the endometrium and have a menstrual cycle. For all other mammals, they get rid of old endometrium in a different way: they reabsorb it if they don't get pregnant.
Vagina Museum
The more common system in mammals is called an estrus cycle. Hormonally, it's very similar to a menstrual cycle, but the key difference is that animals with this form of cycle do not shed the lining of the uterus through menstruation - they reabsorb it.
Vagina Museum
Aside from this, the phases of the estrus cycle are similar to the menstrual cycle. One or more ovarian follicles develop, and the endometrium begins to build up. The animal ovulates, releasing one or more eggs. At this point, either pregnancy occurs, or if it does not, hormonal changes signal that the endometrium isn't needed this cycle.
In animals with a menstrual cycle, at this point menstruation is triggered. In animals with an estrus cycle, the endometrium is reabsorbed.
Vagina Museum
There's a few other general differences between estrus cycles and menstrual cycles. At ovulation, animals with an estrus cycle go into estrus, also known as "heat". During estrus, the animal is sexually receptive, and it usually isn't outside of estrus. Estrus cycles also frequently include a dormant phase, where the animal doesn't have a hormone cycle at all. And finally, estrus cycles tend to happen less frequently than menstruation, sometimes as infrequently as once per year.
Vagina Museum
Dogs are in the majority of mammalian species that have an estrus cycle, not a menstrual cycle. They don't have periods, they instead reabsorb their endometrium.
Vagina Museum
But what about the vaginal bleeding that dog owners notice coming from unspayed dogs? You're not imagining it. It happens. But vaginal bleeding happens at an entirely different point in the cycle!
In a period, bleeding happens when the endometrium is shed. It happens after ovulation. In animals with an estrus cycle, bleeding sometimes occurs - but it happens *before* ovulation. It's a sign that the endometrium is building up.
Vagina Museum
So if you see your dog bleeding from the vagina, it will ovulate shortly afterwards. This bleeding is pretty much the exact opposite of a period!
Vagina Museum
So we're not just being pedantic when we say that dogs don't have periods - the bleeding means something completely different, and you should probably be aware of your pooch's very different cycle if you choose not to have it spayed!
nadja
@vagina_museum I'm sure there's a really good medical reason for it, but I will still reserve being pissed at evolution for making us bleed once a month while there were other options :blobcatSipGlare:
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