Grains Farm produce grains, after all there is plenty of farm fields around but no grain industry.
Animal Farm, grains -> milk and cows (meat).
Food Factory, grains -> goods, milk -> goods, cows -> goods.
You could send grains directly to the factory, but leading them to the animal farm would result in better profit.
I don’t know if the game can handle those ideas, but I would like if it did.