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Bringing sexing back

How to tell the guinea girls from the guinea boys

From Animal Sheltering magazine July/August 2012

Meet marshmallow and her son, Marsh- mallow Junior, two adorable guinea pigs just surrendered to your shelter. They’re lovable and highly adoptable—but Junior seems to be mounting mom quite a bit, and … huh … she seems to be getting a little rotund …

That’s right, you’ve been given a mating pair of guinea pigs! And now there’s so much more adorableness headed your way—up to 10 darling little bundles of joy.

Let’s rewind: Before you end up with your own private G-Force army, consider a little sex ed, guinea pig style.

Guinea girls, or sows, can become pregnant as early as 1 month old. Guinea pig males are able to make time with the ladies when they’re only 3 weeks of age. And for these randy little fellows, mom is in no way off limits. Fertile males shouldn’t be kept in a cage with a pregnant female, because as soon as she gives birth, she’s equipped to be- come pregnant again, so unless you’re adopting guinea pigs out as fast as iPads are selling, you’ll want to enforce an abstinence policy.

Guinea babies are born with eyes open and ready to eat solids (including the requisite unlimited supply of hay), and if you do end up with a new litter, you may want

to call in foster/rescue partners. It’s important to know what sex the pigs are in the first place, though, so you don’t send out a breeding pair.

It’s not easy to determine babies’ gen- ders, but it’s a skill that will help you avoid a population explosion.

Some tips:

Both males and females have nipples, and both sexes will mount, or show dominance.

Baby girls have an indented “V” in the genital region.

Baby boys have the same “V,” but with a ridge on their belly. If you gently press your finger down this ridge, a small penis should extrude. It becomes progressively easier to extrude the older the baby boy gets.

So just remember, when it comes to separating babies from mom, if there’s just a “V,” leave her be. If there’s a lump, he’ll make ladies plump.

You can find photos of piggy privates at all ages at

Now that you’re an expert at guinea genitals (talk about a great addition to your resumé!), congratulations. You can help avoid unwanted pregnancies and keep your shelter from turning into Cute Overload.

About the Author

Shevaun Brannigan is a former Production/Marketing Manager at The Humane Society of the United States.