Microalgae for Feed 163
functions through essential fatty acids. Animals easily digest lipids and common feed sources are mostly
soybean oil, corn oil, fish oil, and by-products.
Proteins
Proteins are present in animal cells and tissues, and are continuously used to replace dying body cells and
supply building body tissues (ligaments, hair, hooves, skin, organs, and muscle are partially formed by
protein). Apart from their important role as a basic structural unit, they are also needed for metabolism,
hormone, antibody, and DNA production. When proteins are fed in excess, they are converted into energy
and fat.
Proteins are complex organic compounds of high molecular weight. As with carbohydrates and
fats, they contain carbon, hydrogen, and oxygen, but in addition they all contain nitrogen and generally
sulphur. Proteins are composed of amino acids, arranged in a linear chain and folded into a globular
form, which are released when the former are hydrolysed by enzymes, acids, or alkalis. Although over
200 amino acids have been isolated from biological materials, only 20 of these are commonly found as
components of proteins. Within all known amino acids, 10 are classified as essential (EAA), as animals are
not able to produce them, and they must be therefore supplied in the diet. Although non-essential amino
acids (NEAA) are not classified as dietary essential nutrients, they are necessary because they perform
many essential functions at the cellular or metabolic level. In fact, they are termed dietary non-essential
nutrients only because the body tissues can synthesize them on demand (McDonald 2002). From a feed
formulation viewpoint, it is important to know that the NEAA’s cystine and tyrosine can be synthesized
within the body from the EAA’s methionine and phenylalanine respectively, and consequently the dietary
requirement for these EAA is dependent on the concentration of the corresponding NEAA within the diet
(FAO 2012).
The requirements of amino acids in animals are well defined in various sets of recommendations
such as those of National Research Council in US. Requirements vary depending on the species and age
of animals. For instance, the dietary EAA for fish and shrimp are Threonine, Valine, Leucine, Isoleucine,
Methionine, Tryptophan, Lysine, Histidine, Arginine, and Phenylalanine (FAO 2012).
Crude protein contains both “true” protein and other nitrogenous products (non-protein nitrogen),
although monogastric animals can only digest the former. However, ruminants are able to convert nonprotein nitrogen into true protein through rumen bacteria. Therefore, this class of animals is theoretically
independent of the dietary protein sources provided, once the rumen microorganisms have become
established (MacDonald 2002).
Animal source proteins are considered as good-quality proteins since they contain a balanced level
of essential amino acids. Plant proteins are thought to be poor-quality proteins because they lack some
amino acids.
Micronutrients
Vitamins
Vitamins are organic compounds required as a nutrient in minor amounts. They are classified as watersoluble and fat-soluble vitamins. The former include vitamins B and C; because they are not readily
stored, a continuous daily intake is important. Vitamin B complex is necessary for body chemical
reactions, and also helps improving appetite, growth, and reproduction, whereas vitamin C helps teeth
and bone formation and also prevents infections. Lipid-soluble vitamins A, D, E, and K, are absorbed
through the intestinal tract. Because they are more likely to accumulate in the body, they may lead to
hipervitaminosis conditions. Vitamin A is associated with healthy eyes, good conception rate, and disease
resistance; vitamin D is related with bone development and mineral balance of the blood; vitamin E is
associated with normal reproduction and muscle development, and can also improve immune system;
finally, vitamin K has a role in blood clotting and prevents excessive bleeding from injuries. Most
vitamins have multiple functions in body, and both deficiencies and excesses lead to diseases.
functions through essential fatty acids. Animals easily digest lipids and common feed sources are mostly
soybean oil, corn oil, fish oil, and by-products.
Proteins
Proteins are present in animal cells and tissues, and are continuously used to replace dying body cells and
supply building body tissues (ligaments, hair, hooves, skin, organs, and muscle are partially formed by
protein). Apart from their important role as a basic structural unit, they are also needed for metabolism,
hormone, antibody, and DNA production. When proteins are fed in excess, they are converted into energy
and fat.
Proteins are complex organic compounds of high molecular weight. As with carbohydrates and
fats, they contain carbon, hydrogen, and oxygen, but in addition they all contain nitrogen and generally
sulphur. Proteins are composed of amino acids, arranged in a linear chain and folded into a globular
form, which are released when the former are hydrolysed by enzymes, acids, or alkalis. Although over
200 amino acids have been isolated from biological materials, only 20 of these are commonly found as
components of proteins. Within all known amino acids, 10 are classified as essential (EAA), as animals are
not able to produce them, and they must be therefore supplied in the diet. Although non-essential amino
acids (NEAA) are not classified as dietary essential nutrients, they are necessary because they perform
many essential functions at the cellular or metabolic level. In fact, they are termed dietary non-essential
nutrients only because the body tissues can synthesize them on demand (McDonald 2002). From a feed
formulation viewpoint, it is important to know that the NEAA’s cystine and tyrosine can be synthesized
within the body from the EAA’s methionine and phenylalanine respectively, and consequently the dietary
requirement for these EAA is dependent on the concentration of the corresponding NEAA within the diet
(FAO 2012).
The requirements of amino acids in animals are well defined in various sets of recommendations
such as those of National Research Council in US. Requirements vary depending on the species and age
of animals. For instance, the dietary EAA for fish and shrimp are Threonine, Valine, Leucine, Isoleucine,
Methionine, Tryptophan, Lysine, Histidine, Arginine, and Phenylalanine (FAO 2012).
Crude protein contains both “true” protein and other nitrogenous products (non-protein nitrogen),
although monogastric animals can only digest the former. However, ruminants are able to convert nonprotein nitrogen into true protein through rumen bacteria. Therefore, this class of animals is theoretically
independent of the dietary protein sources provided, once the rumen microorganisms have become
established (MacDonald 2002).
Animal source proteins are considered as good-quality proteins since they contain a balanced level
of essential amino acids. Plant proteins are thought to be poor-quality proteins because they lack some
amino acids.
Micronutrients
Vitamins
Vitamins are organic compounds required as a nutrient in minor amounts. They are classified as watersoluble and fat-soluble vitamins. The former include vitamins B and C; because they are not readily
stored, a continuous daily intake is important. Vitamin B complex is necessary for body chemical
reactions, and also helps improving appetite, growth, and reproduction, whereas vitamin C helps teeth
and bone formation and also prevents infections. Lipid-soluble vitamins A, D, E, and K, are absorbed
through the intestinal tract. Because they are more likely to accumulate in the body, they may lead to
hipervitaminosis conditions. Vitamin A is associated with healthy eyes, good conception rate, and disease
resistance; vitamin D is related with bone development and mineral balance of the blood; vitamin E is
associated with normal reproduction and muscle development, and can also improve immune system;
finally, vitamin K has a role in blood clotting and prevents excessive bleeding from injuries. Most
vitamins have multiple functions in body, and both deficiencies and excesses lead to diseases.