Do Guinea Pigs Have Periods (Menstrual Cycle)? | Bleeding Explained

Some animals are very similar to humans when it comes to periods or menstruation. The finest example of that is female dogs.

When you see some blood coming from their genitals, that means that the estrous cycle is happening. But what about our female guinea pigs? Are they similar to humans in that field as well?

Do guinea pigs have periods (menstrual cycle)? Guinea pigs don’t have periods (menstrual cycle), but they do have an estrous cycle. These two cycles are completely different, and it is important to note that guinea pigs do not bleed during their estrous cycle.

In this article, we will list all of the reasons why your guinea pigs might be bleeding and talk a little more in-depth about their estrous cycles.

Why Is My Guinea Pig Bleeding? | Possible Causes

Why Is My Guinea Pig Bleeding -Possible Causes

Bleeding from the genitals in some animals is not a cause for concern. However, guinea pigs don’t bleed from their genitals, and if you see that this happened, it’s definitely a reason to visit the vet as soon as possible.
Wondering why your guinea pig is bleeding? Here are the possible reasons:

Urinary Tract Infection

The most common reason for bleeding is urinary tract infection. This is why it’s not strange that many guinea pig owners think that their guinea pig is menstruating.

On top of that, bleeding from the genitals, in this case, is subtle yet can be quite noticeable if you take a good look.

Urinary tract infection usually includes bladder inflammation (cystitis), which can cause the blood to get into the urine. Simply put, blood from bladder inflammation in conjunction with urine causes guinea pig bleeding.

Sometimes the blood appears when your guinea pig tries to urinate, but sometimes, the blood just drips from the genitals, even if the guinea pig isn’t trying to urinate. That’s why we said that it could be quite noticeable.

If you want to make sure that this blood is benign, you’ll need to either take your guinea pig to the vet or try to collect the urine directly from the guinea pig.

The test of your guinea pig’s urine is pretty simple and will show if your guinea pig has a urinary tract infection or any kind of infection that causes bleeding. That’s why it’s very important to notice these symptoms on time, thus making sure that it’s treated well.

Guinea Pig Tumors

Another less common reason for bleeding is the existence of the tumor in the guinea pig’s body or urinary tract.

A cancerous growth, whether malicious or benign, can be very dangerous and almost always cause bleeding. The bleeding from this type of tumor is almost the same as with the urinary tract infection and can easily be mistaken for menstruation.

Since the tumor is probably located somewhere inside the urinary tract, the blood that comes out has a dark red color. Remember that darker blood always comes from the inside and lighter blood comes close to the outside of the body.

The blood from the tumor comes exactly from the tumor itself. The existing tumor can be removed with surgical procedures, and it’s up to the vet to decide whether or not to remove it.

Benign tumors can be removed, but sometimes, the symptoms can be kept to a minimum with medication. Malicious tumors are much more dangerous and require immediate surgery.

The only real way to find out if there’s a tumor is to take your guinea pig to the vet for MRI, ultrasound, and other necessary analysis.


Pyometra is an excessive amount of pus in the uterus. It doesn’t come from the urinary tract but exactly from the uterus, and it can be quite problematic.

In fact, almost every mammal can suffer from this condition, most commonly dogs and cats. The pus in the uterus is a byproduct of a serious infection that can rarely be cured with antibiotics.

Instead, the best solution is an emergency surgery that often involves spaying a guinea pig. Spayed guinea pigs don’t have any potential risks of developing pyometra.


Remember the article where we talked about salt and the potential risks of bladder stones? Well, these exact same stones develop a condition called uroliths, and it’s a pretty common condition that guinea pigs can develop.

Uroliths are caused by an excessive amount of minerals, which turn into microscopic crystals. These microscopic crystals form and develop stones, making your guinea pig bleed.

The bleeding occurs directly from the urinary tract, and in this case, the guinea pig will have a hard time urinating. The tiny mineral particles go through the urinary tract and scratch the walls, making the process of urinating painful and causing bleeding.

There’s nothing to worry about if you visit the vet as soon as possible. However, surgery is the only option here. Your veterinarian will remove the stones that are too large to pass through the urinary tract.

This condition can be prevented by reducing calcium in your guinea pig’s diet, as well as giving them fresh water.

Related: Guinea Pig Illnesses A-Z (Full List of Health Problems)

Guinea Pig Estrous Cycle: Information and Facts

Guinea Pig Estrous Cycle

Is bleeding possible during the estrous cycles of a female guinea pig? As a byproduct of the estrous cycle – the answer is a simple no.

A medical condition in conjunction with an estrous cycle is something that can produce bleeding, but again, the estrous cycle doesn’t have anything to do with the bleeding.

Female guinea pigs’ can be sexually matured at 1.5 to 2 months old, depending on their nourishment. In this case, they will start to go through multiple estrous cycles throughout the year, and it’s important to know something about that as well. 

They go into a heat cycle that lasts anywhere from 14 to 19 days. There are also periods of 12 to 15 hours in which the sow (female guinea pig) is receptive to the boar.

Even when the guinea pig is pregnant, the estrous cycle can still occur. Sometimes the guinea pig can be pregnant while nursing the existing litter.

How Can You Notice an Estrous Cycle in Female Guinea Pigs?

The tricky thing is that guinea pigs often don’t display any kind of signs. Some female guinea pigs will try to mount on other female pigs, which can sometimes be a sign.

Male guinea pigs will, on the other hand, easily notice when a female is in heat period. The male guinea pigs will then chase females often and try to mount them.

That being said, you aren’t going to notice a heat cycle by yourself, but if you have male guinea pigs, they will make things easier for you.

Is Neutering a Guinea Pig Going to Prevent Bleeding

As we mentioned earlier, if your guinea pig gets an infection of the uterus, a great solution is to neuter it.

But, can spaying reduce the risks of potential bleeding? In some cases, yes. Every kind of bleeding that comes from the uterus can be prevented by spaying.

The bleeding that comes from the urinary tract can’t be prevented in that way. The best way of preventing bleeding is to give your guinea pig fresh water with no minerals in it.

Fibers are also a great way to improve overall digestive processes, and since high-fiber food has a lot of water in itself, it’s also great for the urinary tract.

Preventing the development of tumors in the reproductive tract of your guinea pig is also possible. Of course, spaying is a great option, and you should do it after 4 – 6 months of age.

Remember that guinea pigs don’t need to mate, and they can live perfectly fine without it. So, if you plan on keeping only one guinea pig, you should neuter it, whether it’s male or female.

Do Guinea Pigs Have Periods (Menstrual Cycle)_1


Guinea pigs can’t menstruate but can display symptoms that can be mistaken for menstruation, especially for inexperienced guinea pig owners.

A guinea pig can’t menstruate, and the bleeding shouldn’t occur even when in the heat cycle (female guinea pigs). Instead, the heat cycle has different symptoms that aren’t similar to any symptoms we’ve mentioned before.

If you see your guinea pig bleeding from either anus or genitals, you should immediately visit the vet. By determining the cause of bleeding on time, you can save your guinea pig’s life and make the process of curing the disease much easier.

Furthermore, spaying your guinea pig will reduce the chances of any kind of bleeding from the genitals.

Related: Do Guinea Pigs Need Vaccinations?

List of Sources

Neurogenic Inflammation of Guinea-Pig Bladder

A Study of Tumor Immunity in the Guinea Pig

Observations on the Sexual Cycle of the Guinea Pig.