We have 6 Guinea Pigs. One of which was purchased too young (we didn't know how old they were). Well, there were 2 and the first one died and there was nothing I could do about it. The second one was very ill but I mixed baby food (spinach, bananas, etc) with pineapple juice, guinea pig food pellets and vitamin C. I fed her every time I walked in the room. I would dip my finger into the mixture and put it up to her mouth. She started to nibble and soon she would clean my finger off several times. I switched her to a bowl with a spoon full of this mixture and she loved it. Long story short. She is better and all of my piggies like what ever I toss in to them. I give them apples, bananas, spinach, oranges, orange peals and of coarse their normal pellets. We did end up with a dwarf from one of our girls. At birth he was about the size of a very small mouse. His hear was over 1/2 of his body. Jessie has him at her house. Her dad let her have him at home because he is smaller than her hamster. He has no health problems but I wouldn't want more.
