[Nyuko]

When I first brought home my two guinea pigs and gave them salad greens, they ignored the pile and didn't eat more than a nibble. The next day I put out the same pile of salad greens during floor-time, and they cautiously nibbled on a few leaves. On the third day, they devoured it! I think it's really a matter of patience and slow introduction. If they aren't used to eating a variety of vegetables they might not even think it's really something to eat.

After getting them to eat mixed greens, I started introducing other vegetables, like grape tomatoes and bell peppers, and they did the same thing: ignore, ignore, ignore, enjoy!

If you really think the large size and hardness of vegetables could be dissuading your guinea pig, you could cut the vegetables into smaller pieces, but honestly he's probably capable of eating them as they are. Even if he really likes fruits, there's just too much sugar for that to be healthy in the long run.