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Protein
Protein is important for:

building up and repairing various body structures such as tendons,
ligaments and muscles

the structure of enzymes, hormones, haemoglobin, antibodies and
plasma proteins.
Protein is not able to be stored and the excess is broken down in the liver
into energy and urea (which is a waste product of protein metabolism and is
filtered and removed by the kidneys).
Amino acids
Proteins are made up of amino acids. There are 23 amino acids required by
animals.
Of these, some—called the essential amino acids—have to be supplied in
the diet as they cannot be made by the animal.
The other (12–13) non-essential amino acids can be manufactured by the
animal.
Essential amino acids
Animal source proteins contain more essential amino acids than plant
sources hence they have a higher biological value meaning that you would
need to provide less food.
In terms of biological values, dogs require 10 amino acids and cats 11, with
the extra one being taurine.
The more essential amino acids supplied in the food, the higher the
biological value of that food and the less of it that needs to be fed to satisfy
the protein requirement of the animal. Egg has the highest biological value
of 100 and all other proteins are compared to this.
The table below shows some common sources of proteins used in pet foods
together with their biological values:
1
© NSW DET 2007
Animal sources
Biological value

meat–chicken, beef, lamb, fish
80

egg
100

liver
79
Plant sources

soybean
67

wheat
48

corn
45

barley
42
2
© NSW DET 2007
3
© NSW DET 2007