As fruits & things like carrots are higher in sugar, they are only appropriate to feed occasinally or as a treat in smaller amounts. Orange is far form the highest in vit C either. You need to begin feeding the daliy staples.
The daily staples include 1/4 yellow or green bell pepper, this will meet their vitamin C needs. Orange or red contain more sugar & should only be fed occasionally, or when teaching a pig to eat it. 1 slice of red bell pepper does however cover the whole vitamin C intake for the average pig.
2 kinds of lettuce, 2-3 medium/large leaves. Many red & green leaf varieties to rotate. No iceberg, romaine could cause sludge in some pigs & should in that case be avoided.
Cilantro, a great herb that also could be fed daily up to a handful. As well as a chunk of Zucchini if your pigs like it. Feed only these until your pigs eat them well, especially the bell pepper. Then add rotational veggies per Ly's diet chart. This will be the needed cup of veggies.
As well as a good long strand grass hay available 24/7. And a quality pellet, there are only a handful good ones available where most others are pure garbage & harmful. Kleenmamas (best brand, only available online), Oxbow, Sweet Meadow and a certain verison of Mazuri.