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Do Guinea Pigs Have Periods? [Do Guinea Pigs Menstruate?]

Tim Rhodes
Written by Tim Rhodes Last Updated: March 22, 2022

We know that guinea pigs can breed at a very early age. But new guinea pig owners are unsure whether piggies have periods and what to do during that time of a female guinea pig’s reproductive cycle.

Female guinea pigs, unlike most mammals, don’t menstruate (don’t bleed) during their reproductive cycle. Therefore, if a guinea pig pet owner finds blood coming from the female guinea pig’s intimate area, it could be a serious health issue.

Let’s see how guinea pigs reproduce, why they don’t menstruate, and what are some of the common reasons for guinea pigs bleeding.

Why Guinea Pigs Don’t Menstruate?

While most mammals bleed during their menstrual cycle, this is not the case with piggies.

Guinea pigs don’t have a menstrual cycle.

Instead, they have a so-called estrous cycle, which is another type of reproductive cycle that occurs in female mammals.

All mammals have either an estrous or a menstrual cycle that always begins after sexual maturity in the female representative of a species.

In both cases, hormones are responsible for reproduction and they prepare the body of the female to house the fetus during pregnancy.

While primate mammals (and some non-primates) have menstrual cycles, all other non-primates have estrous cycles.

Interestingly, the mammals that have a menstrual cycle tend to mate throughout the sexually active periods of their lives, while those with estrous cycles only copulate around or during ovulation, when they are receptive.

What Is The Difference Between Menstrual and Estrous Cycles?

All mammals have a reproductive tract and a uterus, which has a lining called the endometrium.

Although all mammals have the same body parts, they don’t function in the same way.

There’s a distinct difference between estrous and menstrual cycles in mammals.

This lining changes in size during each reproductive cycle throughout the fertile years of a female as the body prepares the uterus to host an embryo.

In a female with an estrous cycle, the body will reabsorb the endometrium and the female won’t bleed.

Therefore, just like any other female mammal of other species with an estrous cycle, a guinea pig has a uterus that will absorb the endometrium without causing bleeding. 

On the other hand, in other mammals, with a menstrual cycle, the body (or, rather, the walls of the uterus) will shed the endometrium, which causes menstruation (bleeding).

Menstrual Vs. Estrous Cycle (Comparison)

What Is a Normal Reproductive Cycle in Guinea Pigs?

The length of the estrous cycle in guinea pigs is 16 days.

Female guinea pigs are fertile between 6 and 11 hours, commonly during the night.

However, female guinea pigs can begin a new estrous cycle (heat cycle) within 15 hours after giving birth and be ready to mate again while nursing the existing litter.

The gestation period in piggies lasts between 59 and 72 days and most will deliver 2 to 4 babies (rarely, the litter size can count as many as 8 newborns).

Estrus cycles are common in the spring, but a female guinea pig can give birth five times a year.

When Is the First Pregnancy for Guinea Pigs?

A female guinea pig will usually become mature at 2 months of age (or between her 55th and 70th day of life).

Nonetheless, she can become fertile even earlier than that, when she’s only one month old.

The best time for the first-time pregnancy of your pet is before your female guinea pig turns 7 months old because her pelvis is flexible enough to deliver her litter easier. 

As a guinea pig gets older, she loses the ability to widen her pelvis enough for an easier delivery.

What Are the Reasons for Bleeding in Guinea Pigs?

While a guinea pig normally doesn’t experience bleeding during its reproductive cycles, there are several reasons why this small animal could bleed.

Some of the following conditions require emergency surgery.

UTI Or Urinary Tract Infection

Urinary tract infection, which commonly includes bladder inflammation, is common in animals, and it is not hard to identify.

The main symptom is bloody urine, which may seem as if the small animal menstruates, especially if blood appears even when your piggy isn’t trying to pee.

However, male piggies can also suffer from urinary tract infections.

Apart from bloody urine, you will notice that your guinea pig is thirstier than usual, pees much more, eats less, and shows signs of lethargy.

If you see your guinea pig bleeding, the possible reason is a urinary tract infection.

Take your pet to an exotic vet immediately, as he or she will know how to treat these small animals.

Bladder Stones

Bladder stones are one of the most common reasons for a guinea pig bleeding from the bottom.

Bladder stones are microscopic crystals that form and develop stones that cause much pain for guinea pigs, which we’ve covered in another article.

Giving the guinea pig a lot of calcium-rich solid food and bladder infection are the common reason for the occurrence of urinary stones in these small animals.

A guinea pig that acts strangely, has problems peeing, loses weight, and doesn’t drink as much as normally can have a bladder stone problem.

A vet will use an X-ray and ultrasound to confirm the presence of a bladder stone, and will usually advise surgery to remove the stone, as it can be potentially fatal for any guinea pig.

Bladder stones present a life-threatening obstruction, especially in male guinea pigs that can have a stone clogging their penis, preventing the passage of urine.

Female guinea pigs may eliminate the bladder stone from their bodies while urinating.

Rarely, they may retain the stone that can grow into a larger one.

Make sure to feed it only fresh fruits and vegetables safe for piggies that are also low in calcium.

If you notice any of the aforementioned symptoms, don’t hesitate to take your pet to an exotic vet as soon as possible.


Just like unspayed female cats or dogs, unspayed female guinea pigs can also get pyometra, a potentially fatal disease.

As antibiotics are not strong enough to fight off the bad infection, the only option to save the animal’s life is immediate surgery, which is much more complex compared to regular spay procedures.

If your guinea pig has a bloated or swollen abdomen or a discharge from her vagina, she could have a pyometra infection.

You might also notice a sign of your guinea pig losing her fur around the sides and her tummy getting big.

Don’t hesitate to take your pet to a vet, as only a swift diagnosis and treatment can save your pet’s life.

How To Prevent Bleeding In Guinea Pigs?

When it comes to bleeding in piggies due to urinary tract infections and bladder stones, you can do much to prevent such conditions.

Experienced pet owners know that keeping their piggies’ cages clean is essential.

Make sure the bedding is not moist to prevent your piggies from catching a cold or even suffering from potentially fatal ailments, so change it frequently.

Not only you will prevent odor in your guinea pig’s cage but will also prevent your guinea pigs from getting some serious health issues and allergies.

When you keep a guinea pig in a dirty cage, your pet’s feet and body continually touch and rub against the urine and feces, which will cause burns and sickness that worsens over time and causes much pain and discomfort to this small animal.

Dirty and most bedding contributes to bumblefoot, upper respiratory infections, and other serious health issues such as urinary tract infections, even pyometra.

Apart from changing your piggies’ bedding frequently, you will also need to spot clean the corners of your pet’s habitat and hiding spaces. 

Also, make sure to feed your piggies with food low in calcium, to prevent the formation of kidney and bladder stones.

While your baby guinea pig needs unlimited supplies of alfalfa hay, when it grows up, substitute it with an abundance of timothy hay, guinea pig pellets fortified with vitamin C, and a cup of fresh fruits and vegetables that are safe for piggies.

A clean cage and comfortable clean bedding as well as a balanced diet is the key to your pet’s happiness and health.

Final Thoughts

Unlike other animals, female pigs do not menstruate (bleed) during their reproductive cycle. 

Unlike primates, female guinea pigs have an estrous cycle, which means that their uterus absorbs its lining, without causing any bleeding.

So, if a guinea pig owner notices blood, it might indicate a major health problem.

Common health problems that trigger bleeding from the intimate region of a guinea pig include urinary tract infections, bladder stones, pyometra, benign tumors, and cancerous growth.

In any case, now that you know that your guinea pig cannot menstruate, if you notice blood around your pet’s bottom area, consult a vet immediately.


Tim Rhodes
Tim Rhodes

Hi there! My name is Tim Rhodes and I'm a guinea pig enthusiast through thick and thin. My mission is to teach others useful tips and tricks about these cute creatures. When I'm not writing, I enjoy kickboxing and work as an animal trainer.

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