Everybody loves to treat their pigs. That's because pigs love to eat. But you should be very, very concerned about what you're giving them as a treat and when you're giving them a treat. You be sure that you're only treating them when you've asked them to do something and they have done what you've asked them to do. Appropriate treats are in the grain and greens, you can give them a Cheerio - a Cheerio, not a bowl full of Cheerios - but only after they have done something you've asked them to do.
It's very important that you don't continually treat the pig to go from point A to point B, that you're actually treating the pig when it accomplishes what you're asking it to do. And it needs to be one little treat, it doesn't have to be a bowl full of treats. Doesn't have to be a apple, it can be a slice of apple. So keep your treats at a minimum and only in the grain and greens. If you give them green spinach leaves, that's good for them and they probably love it.