Dog coat supplements give the cells of your dog's skin the nutrients they need to stay healthy. Many dogs need a dog coat supplement, as some breeds have higher-than-average nutrient needs. What Are Dog Coat Supplements? A dog coat supplement gives your dog the nutrients and vitamins he needs for healthy skin and a smooth, shining coat. Dog coat supplements contain fatty acids as well as vitamins and minerals. Your dog's supplement needs may vary according to age, breed, level of activity and many other factors. If your dog's skin appears dry and flaky or his coat lacks shine, he may need a dog coat supplement. Dog Coat Supplement Options There are a range of dog coat supplements available including liquid food additives, treats or capsules. Generally, the most effective dog coat supplements contain Omega-3 fatty acids.