I have a 32 quart Presto Pressure Cooker/Canner and just put about an inch of water in the bottom, add a spoon of ACV, take about six Pink Salmon out of the freezer that are frozen whole and use an axe to chop them in half to fit inside the Presto, rinse off the inside of the lid both top and bottom of the rubber seal, heat, exhaust the air, begin timing the cooking process once its between 10-15 pounds of pressure for an hour or two, determined by size of fish so they not only get a warm meal of protein but also have their calcium from the very soft bones...they love it, the geese and ducks eat it, too, with cooked rice added.
Oats are good, you just need to make sure they have grit when you add other food into their diet...