Well, if you are keeping your guinea pig as a pet, there is no option of earning from feeding the guinea pig. However, you can monetize your knowledge of feeding guinea pigs. There are people out there who need to know how to properly feed their little friends.
To earn while keeping your pet, you can have a website where you dish out vital information on caring for guinea pigs generally. There are programs designed to provide a means for you to promote items linking to Amazon. Items linking to Amazon are those that can fetch you a commission when a visitor clicks on them and buys.
As a participant in the Amazon program, they will provide a means for you to earn by linking you with sites to earn advertising. Several bloggers are participants in the Amazon affiliate program. If you grow to an extent, you can earn advertising fees as well.