I would say you need to make up in small quantities as the oils can go rancid quite quickly, especially if stored in plastic tubs in a shed. Years ago we used to put cod liver oil on the grit and mix pink and black minerals with it, but it used to smell off in a few weeks, so only made up enough to last a week. We no longer use cod liver oil haven't done for several years, or brewers yeast don't use that any more either