Back in the 1950s and '60s my father milled his own pig feed. I don't remember the proportions (which varied between pigs of different ages) but I do remember that we used grass meal, and for the weaners, milk powder replaced a proportion of the grain. We didn't add oats as we didn't grow it, but I think soya was in there too. We had a big 'mill and mix' machine in the barn, and stored the meal in cwt hessian sacks.