Vitamin C is a highly unstable compound that breaks down both due to light and temperature. Though the higher quality pellets like Oxbow have stabilized sources of Vitamin C, it does still eventually go bad, and guinea pigs really love their veggies too -- it's a great source of enrichment.
We are as gods to the beasts of the fields. We order the time o' their birth and the time o' their death. Between times, we ha' a duty. - Terry Pratchett.
"Men have forgotten this truth", said the fox, "But you must not forget it. You become responsible, forever, for what you have tamed. - Antoine de Saint-Exupéry