For pets with persistent skin, coat, inflammation or arthritis issues that can't be managed with premium petfoods, vets tend to recommend essential fatty acids and glucosamine supplements to their clients, according to an  article  by The Signal .

Veterinarian Dr. Robert Collett created  The Missing Link , an essential fatty acid supplement manufactured by  Designing Health , in 1994 after realizing that skin, coat and geriatric issues made up close to 80% of his business. The culprit: lack of nutrition, according to the article.

"Dr. Collett started comparing all the dog foods to see what was missing in the modern pet diet. … He began to develop these oil seeds and nutrients that would help to replace what was missing," said Nate Armstrong, vice president of Designing Health.

"Missing Link is only about 3% of a pet's diet. Petfood is kind of like the meat and potatoes, so we're the salad," he said.