Proteins are one of the three macronutrients required in an animal’s diet. Protein can also be used as a source of energy.

Proteins are very large, complex molecules. They play critical roles in almost every aspect of the body; including the muscle mass, enzymes, the immune system, bones, blood, and within cells of the body.


Protein is a source of energy. It provides approximately four Calories (kcal) per gram.2 When carbohydrates are present in the diet they will provide energy and allow protein and fat in the diet to be used as building blocks for the production and maintenance of body tissues, instead of being used for energy production.

Sources of Protein

Proteins can come from many sources. People commonly think of meat as the primary means of providing proteins to the body. However, grains, seeds, legumes, and vegetables are also excellent sources of high quality protein. The protein from one food source will differ from the protein in another food source by the length of the polypeptide chain, the individual amino acids that comprise the protein, and the structure of the folded protein. It should be noted that an individual amino acid from one source (i.e. corn), for example methionine, will be the exact same as that amino acid from another source (i.e. chicken). It is also possible to isolate individual proteins or amino acids and add them to a formula. This would be necessary when a more precise amount of a specific amino acid is needed to meet nutritional requirements, performance requirements or for disease treatment or prevention.

Protein Quality

When evaluating whether a protein is of high quality, both amino acid quantity and digestibility of that protein must be considered. Digestibility determines how much protein can be broken down in the gastro intestinal tract, absorbed into the blood stream, and utilized by the body. Any protein not broken down in the digestive tract will be wasted in the stool. If protein is present in the colon as stool is being formed odoriferous flatulence and loose stool can often occur.

Amino acids are the building blocks of protein. Proteins can be described as a chain of amino acids (similar to a pearl necklace) that folds and turns onto itself to form a 3-dimensional structure. All amino acids share a similar 5-part structure. The distinctive composition of the side chain is what makes each amino acid unique.

Protein digestion begins in the stomach. Stomach acid uncoils the folded protein and specific enzymes break it down into smaller protein chains and individual amino acids. Digestion then continues in the small intestine where different enzymes continue to break down the protein. The individual amino acids get transported from the gastrointestinal tract into the blood to be used by the body to build its own proteins. Digestibility determines how much protein can be broken down in the gastrointestinal tract, absorbed into the blood stream, and utilized by the body.

Essential and Non-Essential Amino Acids

There are two types of amino acids, essential and non-essential. Essential amino acids cannot be manufactured in the body in sufficient quantities, if at all, therefore, they must come from the food. Non-essential amino acids are not any less important than essential amino acids; however, the body has the capacity to manufacture them in sufficient quantities. Dogs have a dietary requirement for 10 essential amino acids, while cats require 11.

1. American Association of Feed Control Officials (AAFCO). 2012. Official Publication.
2. National Research Council (NRC). 2006. Nutrient Requirements of Dogs and Cats. The National Academies Press, Washington, DC, USA.








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