Guinea pigs are a common child's pet and for good reason; they are easy to care for, friendly and rarely bite. Guinea pigs have a unique requirement for Vitamin C in their diet: 10-30mg per animal per day. Many guinea pig diets are sold with the claim that they contain vitamin C. This may be true at the time of manufacturing, however vitamin C in a diet has a shelf life of only 3 months. By the time it leaves the factory, goes through the distributor, into your pet store and into your home, most of the vitamin C is gone. It is therefore necessary to give vitamin C supplements. This is most easily done by adding vitamin C drops or effervescent tablets in the water. Be sure to change the water daily, as once it is suspended in water the vitamin C will only last 24 hours. Guinea pigs that are vitamin C deficient will develop scurvy, which can lead to a whole host of other nutritional problems.