I give our adult pigs two thirds/one third bruised barley to pig rolls, having found the prepared ration a little too rich. I slowly introduce barley to the young ones from about 10 weeks. Make sure the pigs get enough water - you may find they are drinking more - or even soak the barley in warm water for a couple of hours first. This helps digestion. I've not tried oats, but I would imagine it's much the same.
We don't have a problem with them getting fat, but we're in Orkney and keeping weight on the pigs is a full-time job, so you may need to keep an eye on them further south.
And I totally agree with Gareth - it's not a silly question.