I have 7 senior aged papillons ranging in age from 10-15 years, and what goes in their mouths to best maintain heart, brain, bone, and vision health is important. They welcome the addition of this to the bottom of their feeding dishes and lick their dishes clean each day. One tablespoon of cod liver oil contains around 1,360 IU of vitamin D, about the same amount of as 1.5 pounds of sardines or fatty herring. Salmon oil has only 1/5 that amount. Vitamin D is helpful in building strong bones and muscles and helps support the nervous system. Cod liver oil is also three times higher in vitamin A than salmon oil.