This article is one of three articles on protein and its importance in avian nutrition. This first article is about establishing what protein is and its importance in avian nutrition. The second article is about defining the importance protein quality and establishing the balanced protein requirements of birds and the third article is about how do we deliver the correct amount of balanced protein to birds daily.
Protein is a familiar term used in society in general to describe a component of food or feed that is important for healthy living and growth. However, protein is not a single nutrient but a range of complex molecules consisting of number of other individual components called amino acids, linked in various ways. Protein is a nutrient group. Amino acids are the basic units that make up the various proteins and are linked together in peptide chains. These individual component amino acids in turn are composed of the elements carbon, hydrogen, oxygen, sulphur, and nitrogen.
Some proteins have a small number of amino acids linked together and some have many, even hundreds of amino acid units linked together into complex chains and configurations. Some proteins are linked with other non-protein molecules and form complex or conjugated proteins such as nucleoproteins, glycoproteins, and phosphoproteins.
Some of the amino acids can be made by the bird itself and are termed non-essential amino acids, not because they are not important to the bird but because the bird has this ability to manufacture these amino acids in its own body. Other amino acids are termed essential amino acids and cannot be made by the bird but must be provided in the diet fed to the bird. Some amino acids are termed semi-essential and can be made to some degree by the bird but not in sufficient quantities to meet the bird’s daily requirement and therefore a proportion should be provided in the diet.
There are a large range of proteins that function within the body of the bird. Many proteins make up the structural components in the body and these include muscle tissue, feathers, skin, tendons, nails, beak, and cartilage. Collagen, a fibrous protein is the main component of connective tissue within the body. Keratin proteins such as β-keratins are the main proteins that makes up feathers and claws. The protein albumin is present in the blood of birds and enzymes which are involved in all the metabolic processes are also proteins. Many hormones that control many of the homeostatic systems within the body are made up of proteins. Insulin and glucagon are two protein hormones that control normal glucose levels within the blood. Many proteins aid in the absorption of nutrients and act as carriers of other nutrients within the body, such as carriers for minerals. Protein plays a key role in the immune system. Antibodies which develop because of disease challenges are made of proteins.
Protein present in the body is not static but is frequently turned over constantly degrading and renewing itself. The various tissues vary in the rate with which they turnover but all proteins at some stages are catabolised and replaced. During the growth of tissue, the production of eggs and feather development, protein is required to generate this new tissue, the protein in eggs and the feathers.
Crude Protein on Feed or Food Labels can be Misleading
The crude protein recorded on feed/food labels is determined from the total nitrogen level in the food determined by laboratory analyses. The level of nitrogen is multiplied by a factor of 6.25 to give the crude protein level. This is based on the premise that there is 16g nitrogen per 100g protein. Note, this is only an indicative protein level as the level of nitrogen can vary but is usually close to 16g/100g protein for practical purposes. However, this protein figure does not give us any indication as to the quality of the protein in this product or feed ingredient and therefore can be misleading in terms of its ability to provide adequate levels of key amino acids.
Sources of dietary protein and their composition are very important for the development of healthy birds. However, dietary protein from various sources does vary in its amino acid composition.
Dietary protein has several functions.
- Provides essential amino acids for tissue protein synthesis for growth and repair of the various tissues.
- Provides essential amino acids for egg protein synthesis.
- Provide the prime source of dietary nitrogen for the body. Nitrogen is essential to enable the bird to make non-essential amino acids, nucleic acids, purines, and pyrimidines.
- Some amino acids can also provide a source of energy (5.65 kilocalories per gram protein) to the bird.
Understanding the nature of proteins in the body and more importantly the amino acid components of those proteins as well as the nature and amino acid components in feed ingredients fed to birds will allow nutritionists to develop appropriate supplements to properly balance these main ingredients, such as seeds and oilseeds, fed to birds. This has been our approach in developing our TummyRite™ range of supplements and our young bird products, Prosperity™ and StartRite™.
The following table shows lists of non-essential, semi-essential and essential amino acids used by the bird to make various proteins.
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AMINO ACIDS REQUIRED BY BIRDS IN VARIOUS CATEGORIES |
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ESSENTIAL |
SEMI-ESSENTIAL |
NON-ESSENTIAL |
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Arginine |
Glycine |
Alanine |
|
Histidine |
Serine |
Asparagine |
|
Isoleucine |
TaurineϮ |
Aspartate |
|
Leucine |
|
Cysteine |
|
Lysine |
|
Glutamate |
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Methionine |
|
Glutamine |
|
Phenylalanine |
|
Hydroxylysine |
|
Threonine |
|
Hydroxyproline |
|
Tryptophan |
|
Proline |
|
Valine |
|
Tyrosine |
|
Ϯ - Essential in some species. |
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The bird can manufacture new proteins from the essential amino acids provided in the diet and from non-essential amino acids made from nitrogen provided in the diet. It is important to realise that at the cellular level the body does not discriminate from where the amino acids come from, whether from a single amino acid in the diet, or from intact protein in the diet, or from amino acids made within the body. What is clear is that the birds require a minimum amount of certain amino acids to meets its tissue, egg, and maintenance (tissue repair) requirements. It also requires a minimum requirement for nitrogen so it can make non-essential amino acids in addition to those non-essential amino acids also provided in the diet.
In my next article I discuss defining the importance of protein quality and establishing the balanced protein requirements of birds.