1 small serving banana a
week - about the size of a water bottle cap
2 servings of apples and watermelon (low sugar, low acid)
a week
2 small servings a week RAW!!! corn
a week - keep servings far apart
Raw corn husks and silk
every day
1 half baby carrot
a week
In addition to their regular serving of lettuce, green bell pepper, and 1/8th cup of pellets a day.
I suggest you weigh your pig daily and I do not suggest any pig besides a
cuy be over 3.5Lbs.
A guinea pig over 2Lbs-2.5Lbs and keeping a stable weight of 2Lbs-2.5Lbs is not likely to be considered underweight by medical standards.
Please invest in a scale. Here is a good one
http://www.amazon.com/gp/product/B005QRWEBK
Weigh daily, morning and night or before any big feedings and keep a log.
If your guinea pig loses more than 4 ounces in any given time get them to an emergency vet ASAP.
If your pig is not having much appetite due to medications:
http://www.guinealynx.info/probiotics.html
http://www.guinealynx.info/handfeeding.html#preparation
Edited by bpatters: Fruit is not the best way for a guinea pig to gain weight. Sugar can upset their digestive tracts, and make it even more difficult for them to gain. You are far better served by slightly increasing the amount of pellets they get, and making sure they have lots of good fresh hay.
Additionally, while guinea pigs can quickly lose weight if they are ill, it often takes weeks or months for them to regain the lost weight. Be patient, and keep weighing on a regular basis -- once a week is fine unless they're ill. Weigh at the same time of day, preferably before breakfast and record their weights so you'll know what the pattern is.