A male guinea pig is called a boar and a female is called a sow. If you are getting a single guinea pig for a pet, or as a single show animal, it really doesn’t matter which sex you choose. Select a guinea pig that appears healthy, friendly, and not aggressive. A guinea pig that has not been handled may be afraid and try to hide; however, it should not bite when being handled. Handle the guinea pig prior to purchasing to assess its temperament.
If you think you might want to breed guinea pigs once you have more experience, then it is best to begin with a boar as your first animal. A sow must be bred and should give birth before she is seven months old (breeding should take place when a sow is four to six months old). Owning a boar first allows you to take as much time as needed to find a suitable sow for breeding.