I feed unlimited pellets until they reach proper weight. If there are any health concerns, (like with Bob, the bumblefoot pig I had on Baytril for a month) I go to alfalfa pellets for the extra nutrition. I've also given alfalfa hay to an underweight pig in addition to the alfalfa pellets. Always, of course, umlimited hay and water, and the usual amount of veggies. With the change in diet, you might want to give a probiotic if you have any around. It won't hurt to give it. You want the pig to gain weight slowly, not really fast, and just watch his urine to make sure he's handling the extra calcium ok. Back off if the urine is white or gritty. Good luck. I'm still trying to get Bob to gain weight. Maybe now that I've stopped the Baytril he'll gain more. I hate how skinny and frail he looks.