Protein - why is it needed?
Proteins are the main structural constituents of the body’s organs and tissues including collagen and elastin found in cartilage, tendons and ligaments, and keratin proteins in skin hair and nails. Humans and animals need protein in the diet to ensure the healthy maintenance of our bodies.
Protein is also a source of energy and is required by our pets for a healthy immune system, strong bones and muscles so a good quality protein is essential in the diet. In fact, our pets need more protein in their diet than we do (but be careful as too much can lead to kidney damage). Pets also require different amounts of protein in their diet depending on their life stage, for example, whether they are a puppy, pregnant, feeding pups or a senior pet.
New hair and skin require protein and energy for development. Good quality, easily digestible protein is important for normal, healthy skin and hair. A diet low in good quality protein may result in hair losing its colour, skin darkening and/or losing it’s ability to act as a protective barrier (making it susceptible to infection and water loss), poor wound healing, loss of hair and coats that become dry and brittle. Billinghurst (1993, p. 75) states, a protein deficiency leads to “failure to grow or reproduce properly, anaemia, poor hair coat, weak thin muscles, a poorly functioning immune system, bones that do not grow properly”. Other side effects may include infertility, reduced milk production and/or anorexia.
According to McGrath, “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”.
Proteins are comprised of thousands of amino acids. All animals require amino acids for growth, reproduction, strong muscles and bones, a healthy coat and properly functioning immune system. Many amino acids are manufactured in the liver, but some amino acids can’t be manufactured and must be obtained in the diet, these are called essential amino acids. Dietary proteins must be digested so they can be absorbed by the gastrointestinal (GI) tract across the intestinal wall. New skin cells, cells lining the GI tract, and red and white blood cells are produced by the synthesis of protein.
Taurine is an essential amino acid that is critical for normal heart muscle function, vision, and reproduction and is especially important in the diet of cats as they are unable to manufacture it themselves; dogs can manufacture their own taurine, so it is not an essential amino acid for dogs. A taurine deficiency can lead to blindness and/or cardiovascular disease. Methionine is another essential amino acid the body cannot create on its own and is necessary for cell development and growth, is important for skin and coat condition, eye health, heart health and maintaining a pet’s metabolism. The essential amino acid lysine which is necessary for the absorption of calcium from the gut must also be acquired from the pets diet.
Excess protein is eliminated by the kidneys. Long term exposure to excess protein puts strain on the kidneys which overtime causes kidney damage. Unfortunately, as the effects of excess levels of protein takes time to occur it is difficult to attribute this to long term ingestion of an excess of protein (which is often found in commercial pet food).
Sources of high quality protein include meat, bones, eggs, cottage cheese, buckwheat, quinoa and milk. When selecting proteins to feed we look at what is called its Biological Value (BV). The biological value measures a proteins ability to supply amino acids, especially the essential amino acids in the amounts required by the body. The BV is also a measure of how well the protein is digested, absorbed and retained by the body once consumed, in other words the proteins efficiency. Each protein has a different biological value with animal sources (egg, meat and fish) having a higher BV than plant and grain proteins. In fact, whole eggs have a BV of 100, chicken/turkey a BV of 79, beef 78, fish 70 and brown rice 55; making these foods a good source of protein in our pets diet.
Finally, as dogs age they are unable to utilize protein as efficiently, so may require more protein in their diet or supplements in their diet to assist them to digest the protein in their food. According to Schultze (1998, p. 70) advice for a senior dog includes, “a bit of fresh ginger mixed with the veggies can aid protein digestion and acts as a natural anti-inflammatory”.
1. Billinghurst, Dr. Ian, 1993, Give Your Dog a Bone, 22nd Print, Warrigal Publishing, Bathurst, NSW, Australia.
2. Hand, M, Thatcher, C, Remillard, R, Roudebush, P, Novotny, B, 2010, Small Animal Clinical Nutrition, 5th Edition, Mark Morris Institute, USA,
3. McGrath, Jane, How important is protein in a dog's diet?, (n.d.), http://animals.howstuffworks.com/pets/protein-dogs-diet2.htm
4. Schultze, Kymthy, 1998, Natural Nutrition for Dogs and Cats: the Ultimate Diet, Hay House Inc, USA