I wrote a long reply earlier, but the commenting software ate it when it automatically logged me out. The gist of it was vit C is made by dogs but a little extra might help a senior dog, cod liver oil supplies vit A in large amounts and vit D, which are fat soluable vitamins that the body can’t get rid of if you give too much so I wouldn’t add them to kibble much, Magnesium is supposed to be balanced with zinc and calcium and I don’t know what the ratio is. I really like to add a super green to my dogs’ foods like spirulina or kelp, they have loads of micronutrients that the dog food manufacturer are not required to make sure the dog food has.
