I was under the impression that given the right amount of a good quality pellet such as the Burgess ones and a variety of fresh veg (bell peppers, brocolli, kale are all good for vitamin C but we wary of giving too much of the latter two due to calcium content) vitamin C supplements weren't really necessary. I can understand supplementing when a pig is ill and it's not going to do any harm the rest of the time but do they really need it supplemented?