Identifying a guinea pig's gender isn't instantaneous, and it's rarely easy. Cavies don't offer many visual clues. If you know what to look for and you look closely, you may be able to determine the sex of a guinea pig, whether you examine the nipples, the genital region or both.
Follow a proper protocol when handling your guinea pig when you attempt to identify the gender. Be delicate, foremost. A pet who feels frightened may squirm and attempt to run away. Play it safe by conducting your examination on a surface that's low to the ground. That way, if your cavy somehow gets out of your hands, he will not get hurt. If at all possible, recruit the assistance of a friend or family member. A friend will be able to securely hold your guinea pig with her hands circling the shoulders and chest, helping you get a closer and more stable look. Abstain from making loud noises or jarring movements as you examine your cavy. Have your helper seat the guinea pig on his rear end over a soft towel, and make sure his back has plenty of propping.
Boars, which are male guinea pigs, typically are slightly bigger than their female or sow counterparts. Their bodies are usually a little bit longer, as well. Fully mature, adult male guinea pigs usually weigh around 700 grams, while adult female guinea pigs weigh around 450 grams. If you can get your guinea pig on a gram scale, his weight may be able to provide you with helpful gender hints.
Take a close look at your guinea pig's genital region. If the fluffy one is indeed female, you may notice an orifice that has a conspicuous "Y" shape. In the center of the opening, you may spot a small ripple, as well, although not always. Boars, on the other hand, possess prominent scrotal pockets. If you softly apply pressure on a guinea pig's lower belly, it may trigger the penis to appear. In the event that nothing happens, you probably have a female on your hands. Before you even push down on the belly of a boar, you may detect a stiff bump of sorts.
A quick glance at the nipples can be useful for gender identification. Sows, in general, possess much larger and more noticeable nipples than boars.
Help From a Veterinarian
If you want a little extra help in figuring out a guinea pig's gender or perhaps need help in handling an especially jittery cavy, take him to the veterinarian for gender identification purposes. Find an exotic veterinarian who has abundant experience with cavies.