gaining weight

Question
hello!
my guinea pig, andre is going to be 5 years old in april. we got him when he was (approximately) six weeks old. he has always been tiny, i was thinking it's possible that he could have been the runt of his litter (i'm not sure if that's even possible with guinea pigs or not) when i compare him to other boars he just seems so little! we weigh him weekly, stays at 2.2 pounds, and i have read that it is a healthy weight for his age.

my question is, is there a healthy way to make him a little chunkier? like i said, he has always felt a little bony just because he is so little but i'm wondering if he is just too skinny. his little hipbones are pretty prominent when we are petting him. he eats a steady diet of romaine lettuce, fresh timothy hay, and we get him vitamin c fortified food (he always picks out the dried carrots and treat first before getting to the actual pellets)

he is perfectly healthy, eats a TON, and stays pretty active and vocal for a five year old boy. just want a little more junk in the trunk:) or if you could tell me if it's normal for him to be so bony!

thank you!

Answer
Just like people not all animals will get fat. It sounds like he's an active and healthy pig. 2 pounds is an average size for an adult pig.  As pigs age they often start to thin down more than when they were younger. You rarely see obese elderly humans. And you don't often see obese old pigs. There are exceptions to everything of course, but as a rule older pigs are seldom overweight.

Humans are rarely obese at an old age because obesity doesn't allow them to reach that age. They typically succumb to their obesitiy with heart attacks, diabetes, and other conditions that take them before they get old.

Five is an average lifespan for most guinea pigs. Andre has reach the time in his life when he is considered elderly. If he's eating normally he is still healthy, so I wouldn't worry about him getting thinner. The appetite is the gold standard for how a pig feels, and he obviously feels very good or he wouldn't be eating like he is.

There really isn't any diet or foods you can give him to fatten him up. You've done a marvelous job of keeping him healthy for five years. Just continue what you're doing and don't worry about trying to put more fat on him. He doesn't really need it.