Gendering guinea pigs: how to tell if your guinea pig is male or female

Why does sexing guinea pigs matter?

Getting the sex of your guinea pigs right is one of the most important things you can do as an owner.

An unneutered male and female housed together will breed rapidly. Females can become pregnant again within hours of giving birth, and pups can themselves breed from just a few weeks old.

Unplanned litters can quickly become unmanageable for their owners. Do not rely solely on a breeder or pet shop to confirm the sex. We recommend always checking for yourself or asking your vet.

What are boars and sows?

Male guinea pigs are called boars, females are called sows, and babies are called pups. Boars are usually slightly larger than sows, but size alone is not a reliable way to tell them apart.

How do you tell the sex of a guinea pig?

The most reliable way to sex a guinea pig is to gently examine their genital area. It’s easiest if two people do it – one to hold and one to check.

As the holder, place one hand under the guinea pig’s chest and support their bottom with your other hand – gently holding them upright against your body.

Female (sow)

A female’s genital area has a Y-shaped opening. The base of the Y is the vulva. There is no raised ridge above the opening, and gentle pressure will not cause anything to emerge.

Male (boar)

A male’s genital area has more of an i-shape – a slit with a small round dot above it. That dot is the retracted penis. Applying gentle pressure just above the opening should cause the penis to emerge slightly, confirming the sex. In older boars, the scrotal pouches on either side of the genitals are often visible.

Sexing very young pups can be tricky as their genitals are small and may appear swollen shortly after birth. If you’re unsure, wait until two to three weeks of age when differences become clearer, or ask your vet to check.

Young male guinea pigs should be separated from mum and any female siblings when they are weaned at three weeks of age.

Keeping guinea pigs safely

Once you know the sex, you can plan their housing safely. Good housing combinations include:

• Two or more females – sows usually get along well in pairs or groups.
• Two males – a pair of boars can live together, especially if they’re siblings or introduced young. Avoid groups of three males, as conflict is more likely.
• A neutered male with one or more females – this can work very well, but neutering must be carried out by a vet. It takes around six weeks after the procedure for a male to become sterile.

Spaying females is a more complex procedure and is usually only recommended for health reasons such as ovarian cysts. Speak to your vet about the best neutering option for your guinea pigs.