Just feed the hogs you want to keep a sow feed for a couple weeks prior to slaughter, that should put some needed fat on them. Just about everything we buy at the fair comes home and eats for a few weeks, more because the butchers in the area are flooded with animals at that time of the year, and I won't send them to the state plant to get killed, too much stress on them for me. You can put fat on hogs fairly quick with a feed with higher fat content and less protein.
You need to feed them a show type feed to compete; it sure does make them look different than a commercial complete feed. I would stay away from the feed with paylean if you can, it does tend to make the meat dryer. The biggest on hogs is they need to be walked every day to make sure they are in shape, a hog lying in the corner of the show ring panting like a worn out dog, does not do well. We made the boys walk them for ½ hour a day up and down the pasture. You start out slow and work them up to the half hour a day. We did in either morning or evening as it started to cool off.