How to Determine the Sex of Your Guinea Pig

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Tell if your guinea pig is male or female with our helpful guide

Co-authored by Pippa Elliott, MRCVS

Last Updated: November 21, 2024 Approved

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Examining the Guinea Pig

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Identifying the Guinea Pig’s Sex

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Many pet owners have difficulty determining the sex of their guinea pig, especially in newborn guinea pigs.^{[1]
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Research source} Identifying the sex of your guinea pig can help you to prevent unplanned pregnancy if you introduce another guinea pig into the mix and let you know if you'll need to separate a baby from its mother.^{[2]
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Research source} Though many vets offer sexing services for guinea pigs, you can also determine the sex of your guinea pig on your own.

Things You Should Know

Before examining your guinea pig, be sure to wash your hands and put on gloves.
Examine the distance between your guinea pig’s anus and genitals. Male guinea pigs have more space between their anus and genitals, while females tend to have less.
Look closely at the cavy’s genital opening. Female guinea pigs usually have swelling over their genital area, while males have a small circular dot with a penis above.

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Examining the Guinea Pig

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Be careful when examining very young cavies. Newborn cavies can become distressed when away from their mothers, and they are much more delicate. They also get cold easily, so when you examine them, do so in a warm area and try to be as fast as possible.
- It can be extremely difficult to determine the sex of a very young guinea pig. You can wait until the guinea pig is 2-3 weeks old to sex it, at which time it is easier to determine the sex ^{[3]
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  Research source}. However, since males must be separated from their mothers and sisters at 3 weeks old, it is crucial to sex them by this time. Otherwise, they can impregnate their mothers and sisters.
- Don't worry about handling young guinea pigs. Their mother will not reject them and early handling can help make them less afraid of humans. ^{[4]
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Wash your hands before and after handling. Guinea pigs can carry diseases that infect humans and they can be affected by things on your hands (hand sanitizer, lotion, etc.), so it is important to wash your hands often.
- Don't worry about wearing gloves. Very few human diseases can be given to guinea pigs and they do little to stop diseases from spreading from pig to pig.
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Cavies are often squeamish about being picked up and held in place for a long period of time. Put a soft, clean towel on a low, stable service, like a low table or the floor in preparation for the exam so your guinea pig is protected and comfortable.
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Hold the guinea pig gently but firmly. Guinea pigs are easily scared and will often struggle when frightened. Avoid freaking out your cavy by holding the cavy firmly but gently around the chest and shoulders. Place the guinea pig on the back or the rump, so the stomach and genital area are facing you and cradle the cavy’s back with one hand. This will make it easier for you to examine the cavy’s genitalia.^{[5]
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- Cavies dislike being on their backs for a long period of time. Try to do the examination quickly and efficiently. You may want to ask someone to help you hold the cavy while you conduct the examination to speed up the process.
- Give your guinea pig a treat while doing this. It will make them easier to work with and less scared.

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Identifying the Guinea Pig’s Sex

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Check the distance between the guinea pig’s anus and genitals. Start by looking for the cavy’s anus, which is a vertical opening that is often gray or brown colored. The anus will be located underneath the cavy’s genitalia.^{[6]
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- Once you have distinguished between the cavy’s anus and the cavy’s genitals, you can look at the distance between the cavy’s anus and the cavy’s genitals. Female guinea pigs have a shorter amount of space between their vulva and their anus. Often, the vulva sits right above the anus in female cavies. Male guinea pigs have a larger amount of space between their penis and their anus, about 2-3cm of space between the penis and the anus.
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Examine the shape of the cavy’s genital opening. Look closely at the cavy’s genital opening. Female guinea pigs usually have a smooth swelling over their genital area. Use your fingers to part the genital opening gently. If the genital area forms a “Y” shape, this means the cavy is female.^{[7]
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- Male cavies have a genital opening that is shaped like a small circular dot with a penis raised above the level of the surrounding skin.
- Male guinea pigs have a bulge to their genital and anal areas. The bulge appears due to the presence of the guinea pig’s testicles, which are just under the skin along the anus and the penis. You should also check if there is a donut shape around the cavy’s anus, as this is where a male cavy’s testicles will sit.
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Press just above the genital opening to check for a penis. Sometimes it can be difficult to see the penis, especially in heavy older male cavies. To make the penis protrude, use your finger to gently press just about the guinea pig’s genital area. The penis should show itself.^{[8]
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- You can also use your finger to gently press and rub just over the genital area. If you feel a “ridge” just over the genital area, you are feeling the inner part of cavy’s shaft. This is a clear sign the cavy is male.
- While checking for the penis, look and feel for testicles on either side of the penis to confirm that the pig is a male. The testicles are rather large relative to the size of the pig's body.
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Have a licensed vet confirm the guinea pig’s sex if you are unsure. It is notoriously difficult to confirm the sex of guinea pigs, even with a careful and thorough examination at home. If you are not 100 percent certain of your guinea pig’s sex, you may want to bring your guinea pig to the vet for an examination. Go to a vet you trust and/or a vet who has examined your guinea pig before, as even knowledgeable vets can wrongly determine the sex of a guinea pig.^{[9]
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- You may also want to bring your guinea pig to the vet if your guinea pig appears distressed during the examination or reacts poorly to the exam. It may be difficult to get an accurate reading of the cavy’s sex if the cavy is stressed out or moving around a lot during the home exam.