I recently got into this discussion and found out that fish oil will interfere with vitamin E absorbtion so it is really important to either use a fish oil that has it added or add a vitamin E pill on the side. If you look at the ingredients, the vitamin E will be listed as dl- alpha tocopherol (sp?). The "dl" in the begining means that it is a synthetic form and just "d" is the natural form. The synthetic form is only half as effective so if you can get the natural it is better.
Also, try to avoid one that has soy in it. I guess soy is a really common allergy cause in dogs. I used the Costco generic version with soy in it and my dogs were fine so if you do get that one, just watch your dog at first. If they get itchy and rashy, you'll have to switch to something else. My dogs love the fish pills, when they eat them, you here a popping sound. My husband is so sensitive, he gags at the sound! :lol: :roll: