my guinea pig is recovering from an UPI

Question
i adopted a guinea pig today who is recovering from an UPI (upper respitory infection) and he is very under weight. he just got off his antibiotics a few days ago and i don't know how to fatten him up. he is probaly 9 weeks old and a little bit under a pound. he needs to gain weight and i think he is just getting his eating habbits back. is it ok to give him fruits and veggies since he is recovering or is too young? is there anything i can use to help him recover and gain weight quicker?

Answer
Emily,

You can give him veggies, and a small amount of fruits. As fruits contain high sugar and can cause diabetes in Guinea Pigs. Some good veggies and fruits to feed him are as fallows,

Asparagus
Brussels Sprouts
Celery
Cilantro
Collards
Corn, White
Cucumber (with skin)
Dandelion Greens
Green Beans
Mustard Greens
Okra
Parsley
Parsnips
Peppers, Green
Peppers, Red
Pumpkin
Spinach
Squash (summer, all varieties)
Squash (winter, all varieties)
Sweet Potato Leaves
Sweet Potato
Swiss Chard
Tomato
Turnip Greens
Turnip

And some other good fruits are these,

Apple (with Skin)
Apricots
Banana
Blackberries
Blueberries
Cherries, Sweet
Cranberries
Grapefruit, Pink and Red
Grapefruit, White
Lemon (no peel)
Lime
Nectarine
Orange
Peach
Pear
Pineapple
Plum
Raisins, Seedless
Raspberries
Strawberries
Tangerine

Alfalfa Hay will help in fatting him up. So feed him that, in all reality he'll need that till he is about 10 months then you'll want to mix it half and half with timothy so that by a year he can be switched over to straight Timothy hay. Also the antibiotics he was on have destroyed the good bacteria in his stomach that help him to digest foods properly and that is why he is so thin, so to help replace that bacteria give him a supplement of lactobacillus acidophilus (you can find this in health food stores) or live culture yogurt. That'll help in getting him to put on weight quicker.

I hope this helps,
  Take care,
    Jules