As we mentioned earlier, amino acids in proteins make up the building blocks of skin tissue and hair, among other things. Dogs' hair contains about 65 to up to 95 percent protein [source: Schenck]. So, it makes sense that dietary protein intake has a big effect on a dog’s skin and coat.
Proper dietary protein helps maintain a dog's healthy skin and a full coat. In particular, for hair to grow well, it needs sulfur-containing amino acids. Dry or brittle fur and patches of hair loss can be a sign that your dog needs more protein in his diet. Protein deficiency also causes skin darkening or depigmentation of hair. The damage to skin can itself be a danger to the dog, as it weakens the skin's ability to protect against infections and heal wounds.
It also stands to reason that a dog's protein needs can vary depending on whether the dog has long hair or short hair. Consider that a long-haired dog could use up about 30 percent of the protein it consumes just on hair growth alone. A short-haired dog might use about 10 percent of its dietary protein for hair [source: Schenck].
So, how much protein does a dog need? Average adult dogs need about 18 percent of their calories to be from protein. Puppies generally need about 22 percent protein. Active dogs, as well as pregnant and lactating females, also need extra protein in their diet. Many senior dog foods contain reduced protein. However, unless your vet recommends a low-protein diet, older dogs need just as much protein as ever. In fact, some experts say that they need even more protein as they age [source: National Academies].
Because of the various factors that go into determining how much protein your dog needs, be sure to talk to your vet about the best diet. And remember to alter that diet depending on life stages.