I don't even mess with medicated feed at all. The closest I will come is using wormer pellets, I mix them with their feed and that is only when I change up from using tobacco to worm them.
I have read quite a bit on additives and I have seen the results of what they can do. I saw several pigs at a show that looked like walking muscle bound chunks of meat! I doubt you could have scraped a pound of fat off of a few of them! I'm not a fan of that look, instead I want that layer of fat to serve as protection and give them a natural appearance; in short I like a hog that looks like a hog.
IF you are interested in giving your stock a little extra- consider the vitamin A from fruits/vegetables, lysine from eggs, soured corn, milk or dried distillers grains. Any of those added to their rations will affect the appearance of your hogs. I know I harp on the same things time after time but they really do work.
I have heard of some farmers seeing really nice results by adding a percentage of rice to their hogs rations, the biggest drawback is that feeding rice can lighten the color of their meat- but if you don't mind that then it could be an option. Check around and see if you have a day old bakery in the area, you can feed old baked goods to your hogs and I doubt they'll object.
I was talking with a buddy of mine yesterday and he is going to take cull sweet potatoes (sold locally as stock feed, very cheap!) and put them through a feed grinder with some fresh hay and make a form of quick silage. It should be highly nutritious and he'll need to monitor the moisture level but that is a quick and easy feed. Some folks talk about baling milo after cutting the seed heads off, it is said to make quality feed that is rapidly consumed and puts good weight on; IF you can find it, I suggest you get a few bales of milo hay and hold it back in case you need to get a critter into shape or fleshed out in a hurry.
I have been playing around with making my own haylage, I tested some and it smells carmel-like and my goats nearly ate my hand off to get it. If I continue to see good results I'll tell you how I made it, it is packed with nutrients.
Only if needed. Auromyacin(sp?) mixed in ground feed according to instructions when we have foul weather piglets, and only from weaning up to a month long if its nasty weather. A stitch in time ...
I grind a pelleted vitamin and mineral supplement (Milk Plus) there is also (Calf Mana) that is the same thing. I add 5 lb to 100Lb of ground grain. I grind 2 parts peas 1 part wheat and 1 part barley. To that I add 1 1/2 cups DE.