Posted on: 2010-04-20

Animal nutrient requirements



Feed is material which, after ingestion by animals, is capable of being digested, absorbed and utilised. In a more general sense is edible material, components capable of being utilised by animals or nutrients (McDonald, 2002).

The animals associated with man cover the spectrum from herbivores, the plant eaters (ruminants, horses and small animals such as rabbits and guinea pigs); omnivores, which eat all types of foods (pigs and poultry); to carnivores, which eat chiefly meat (dogs and cats) (McDonald, 2002). In addition, animals are also classified regarding their digestive system. In simple terms, the digestive system is a portal for nutrients to gain access to the circulatory system. The specific feedstuffs animals are able to utilize is dependent on the type of digestive system they possess. There are three basic types of digestive systems: monogastric (simple stomach), ruminant (multi-compartment stomach) and hind gut fermentor (simple stomach but very large, and complex large intestine) (Coffey, 2008).

Examples of each class are:
• monogastric animals - include humans, chickens, turkeys, pigs, dogs and cats;
• hindgut fermentors - horses, rabbits and ostrich;
• ruminants – beef and dairy cattle, goats, sheep and deer.

Feeds are blended from various raw materials and additives. These blends are formulated according to the specific requirements of the target animal. They are manufactured by feed compounders as meal type, pellets or crumbles (Wondra, 1995). The main factors influencing the nutritive value of a diet are the ingredients employed and their chemical composition (McDonald, 2002).

Animals need a variety of nutrients to meet their basic needs. These nutrients include fats and carbohydrates that provide energy, proteins that furnish amino acids, vitamins that serve as co-factors for enzymes and perform other functions, ions required for water balance and for nerve and muscle function, and selected elements that are incorporated into certain molecules synthesized by cells (Freeman, 2003).

These nutrient classes can be categorized as either macronutrients (needed in relatively large amounts) or micronutrients (needed in smaller quantities). The macronutrients are carbohydrates, fats, fiber, proteins, and water. The micronutrients are minerals and vitamins.

The main components of feeds, plants and animals are described in figure 3.


Nutrient properties

Carbohydrates are chemical compounds essentially of carbon, hydrogen and oxygen, made up of sugars, starches, cellulose and lignin. The main functions of this nutrient are as energy that powers the muscular movement, as a source for body heat, as building block for other nutrients and its dietary excess is stored as fat. Simple carbohydrates (sugar and starches) are referred as nitrogen free extract and are mostly present in cereal grains (corn, etc). Complex carbohydrates (cellulose and lignin, also called fiber) are difficult to digest and can be found mostly in roughages (hay, grass, etc).

Carbohydrates utilization by animals depends on their digestion system. Simple stomached animals cannot digest large amounts of fiber, and their ration must be made up of mostly cereal grains. Ruminant animals can eat large amounts of fiber, and a high percentage of their ration is roughage.


Fact 1 ________________________________________________________________

Carbohydrates in algae can be found in the form of starch, cellulose, sugars and other polysaccharides, which will improve the metabolizable energy of the feed with an algae supplement.
The cellulose content will affect the digestibility of the algae by non-ruminant animals, but the reported algae tests performed so far indicate that their overall digestibility is good (Becker, 2004).



Lipids (fats or oils), as well as carbohydrates, are neutral chemical compounds essentially of carbon, hydrogen and oxygen, but contain more carbon and hydrogen atoms than carbohydrates. For this reason fats have 2.25 times as much energy value than carbohydrates. At body temperature fat are solids and oils are liquid. The main functions of this nutrient are as energy source (stored at higher conc./g than carbohydrates), as a source of heat, as insulation, as body protection (cushioning), as carrier of fat-soluble vitamins and has an immune function trough essential fatty acids. Lipids are easily digested by animals. Lipids for feed sources are mostly soybean oil, corn oil, fish oil, and by product fats (lard or tallow from livestock rendering).


Fact 2 ________________________________________________________________

Algae average lipid content varies between 1 and 40 %, and under certain conditions it may be as high as 85 % of the dry weight (Becker, 2004).
Some algae are often utilized for aquaculture for their high content of w3 and w6 polyunsaturated fatty acids (PUFA).  



Proteins are complex organic compounds of high molecular weight. As with carbohydrates and fats, proteins contain carbon, hydrogen and oxygen, but in addition they all contain nitrogen and generally sulphur (McDonald, 2002). Proteins (also known as polypeptides) are made of amino acids arranged in a linear chain and folded into a globular form. Amino acids are produced when proteins are hydrolyzed 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. Animals cannot synthesize the amino group, and in order to build up body proteins they must have a dietary source of amino acids. Within all known amino acids, there are 10 classed as “Essential Amino acids”, as the animal can’t produce them. Non-essential amino acids are also needed by animals, but are synthesized from other amino acids. Proteins are present in animals cells and tissues, and are continuously needed to replace dying body cells and to supply materials to build body tissue (ligaments, hair, hooves, skin, organs, and muscle are partially formed by protein). Thus, proteins have an important role as basic structural unit, and are also needed for metabolism, hormone, antibody and DNA production. When proteins are fed in excess, they are converted to energy and fat. 

Crude protein contains both true protein and other nitrogenous products (non-protein nitrogen), but only the true protein portion is able to be digested by animals. However, contrarily to monogastric, ruminants are able to convert non-protein nitrogen to true protein by rumen bacteria. Also, in the case of ruminants, all the essential amino acids can be synthesized by the rumen microorganisms, which theoretically make this class of animals independent of a dietary source once the rumen microorganisms have become established. However, maximum rates of growth or milk production cannot be achieved in the absence of a supply of dietary amino acids in a suitable form (Mac Donald, 2002). Non-ruminant animals cannot synthesize the essential amino acids fast enough to meet the animals needs, therefore those essential amino acids must be provided in the ration. 

Animal source proteins are considered good-quality proteins since they contain a good balance of essential amino acids. Plant proteins are thought to be poor-quality proteins because they lack some amino acids. Ruminant’s protein requirements can be met by feeding proteins of vegetable sources and also by feeding urea (synthetic nitrogen source made from air, water and carbon). Urea is mixed with the ration to provide nitrogen for making amino acids in the ruminant body. Monogastric organisms need balanced ration with the right balance of essential amino acids. If grains are combined in the correct combination they will provide a balanced ration. Soybean meal is most commonly used.

Fact 3 ________________________________________________________________

Microalgae proteins have an amino acids profile comparable with the best protein sources (Chlorella is better than soybean in most essential amino acids).



Vitamins are organic compounds required as a nutrient in tiny amounts by an organism. Their classification is divided in two categories: water soluble and fat soluble vitamins. Water-soluble vitamins, vitamins B and C, dissolve easily in water. Because they are not readily stored, consistent daily intake is important. Vitamin C helps teeth and bone formation and prevents infections, and vitamin B complex is needed for chemical reactions in the body and helps improving appetite, growth and reproduction. Lipid-soluble vitamins, vitamins A, D, E, and K, are absorbed through the intestinal tract with the help of lipids (fats). Because they are more likely to accumulate in the body, they are more likely to lead to hypervitaminosis than are water-soluble vitamins. Vitamin A is associated with healthy eyes, good conception rate, and disease resistance, vitamin D is associated with good bone development and mineral balance of the blood, vitamin E is associated with normal reproduction and muscle development and can also help immune system, and vitamin K helps with blood clotting and prevents excessive bleeding from injuries. Most vitamins have multiple functions in body involving metabolism, enzyme reactions, etc, and both deficiencies and excesses lead to disease. 


Fact 4 ________________________________________________________________

Microalgae represent a valuable source of nearly all important vitamins which improve the nutritional value of algal biomass (Becker, 2004).



Minerals in feed are the chemical elements required by living organisms, other than the four elements carbon, hydrogen, nitrogen, and oxygen that are present in nearly all organic molecules. They are needed in small amounts and may be classified regarding its nutrition requirement rate as major or trace minerals. Some dietitians recommend that these be supplied from foods in which they occur naturally or at least as complex compounds, or sometimes even from natural inorganic sources (such as calcium carbonate from ground oyster shells). Some are absorbed much more readily in the ionic forms found in such sources. On the other hand, minerals are often artificially added to the diet as supplements; the most famous is likely iodine in iodized salt which prevents goiter. Minerals provide material for growth of bones, teeth, tissue, regulate chemical processes, aid in muscular activities, release energy for body heat, protein synthesis, oxygen transport, fluid and acid-base balance in body, enzyme reactions, and many other benefits.


Other micronutrients include antioxidants and phytochemicals which are said to influence (or protect) some body systems. Their necessity is not as well established as in the case of, for instance, vitamins. Phytochemicals may act as antioxidants, but not all phytochemicals are antioxidants.

Antioxidants are a recent interest area. As cellular metabolism requires oxygen, potentially damaging (e.g. mutation causing) compounds known as free radicals can form. Most of these are oxidizers, some reacting very strongly. For normal cellular maintenance, growth, and division, these free radicals must be sufficiently neutralized by antioxidant compounds. Recently, some researchers suggested an interesting theory of evolution of dietary antioxidants. Some are produced by the human body with adequate precursors (Vitamin C) and those the body cannot produce may only be obtained in the diet via direct sources (Vitamin C in humans, Vitamin A, Vitamin K) or produced by the body from other compounds, as Vitamin D synthesized from cholesterol by sunlight and Beta-carotene converted to Vitamin A by the body.


Fact 5 ________________________________________________________________

During the 1970s, researchers realized that under certain culture conditions Dunaliella will accumulate high amounts of dry-weight as B-carotene. This discovery led to commercial derivation of natural B-carotene from this organism, which is currently a substantial and growing industry (Becker, 2004).



Phytochemicals and their subgroup polyphenols are the majority of antioxidants; about 4,000 are known. They represent a growing area of interest is the effect upon human health of trace chemicals, collectively called phytochemicals. These nutrients are typically found in edible plants, especially colorful fruits and vegetables, but also other organisms including seafood, algae, and fungi.


Fact 6 ________________________________________________________________

Microalgae are sufficient for proper nutrition for it contains adequate to rich amounts of the essential amino acids as well as most fat- and water-soluble vitamins needed by animals.



Each animal has a specific set of nutrient requirements. Some examples of the nutrients requirements of production animals, aquaculture, pets and other are presented in next table.

Table 1. Nutrient requirements for several animals

Click image to zoom

Markers description:

 1 - Nutrient requirements for maintenance of cows producing 20 kg/day milk of 38 g and 34 g protein/kg and weighting 550 kg  (McDonald et. al., 2002); CP estimated based on (NRC, 2001); Amino acids requirements        estimated based on (Merchen and  Titgemeyer, 1992)                                                                                                                                                                                  2 - Recommended nutrient levels of swine during gestation, with weight between 100 and 200 kg (Goodband et. al., 1997)                3 - Recommended nutrient levels for laying of leghorn-type chickens (Firman J., 1984)                                                                        4 - Recommended nutrient levels for feeding Rainbow Trout with 575 g, adapted from (NRC, 1993)                                                    5 - Nutrient requirements for maintenance of adult dogs with 15 kg, adapted from (NRC, 1985)                                                            6 - Nutrient requirements for intense work horses with 600 kg of live weight (McDonald et. al., 2002)


DMI – Dry Matter Intake: all the nutrients contained in the dry portion of the feed consumed by animals. Dry matter intake can be measured in feeding studies by weighing the total ration fed and the amount of feed left by the animal. Feeding studies have shown that as the percent of neutral detergent fiber (NDF) increases in forages, animals consume less. Therefore, the per cent NDF can be used to estimate dry matter intake (DMI (as a per cent of body weight) equals relative feed value as per cent of body weight divided by per cent NDF). DMI (% of body weight)=120/NDF (% of DM).

ME – Metabolizable Energy: is the digestible energy intake minus the energy in the urine minus the energy in the gaseous product of digestion: ME = DE - (energy in urine) - (energy in gaseous product of digestion). The ME value of individual feeds is rarely measured. Measuring the amounts of energy lost in gaseous form and in the urine is more difficult than measuring digestible energy. Therefore, conversion formulas are often used by nutritionists when ME values are needed. The common formula used to estimate ME in beef feedstuffs is ME = 0.82 x DE.

MP – Metabolizable Protein: is protein (amino acids) that is actually absorbed from the gut. MP consists of protein in the rumen microorganisms, feed protein and any protein that bypasses digestion in the rumen (undegradable intake protein (UIP). The concept of protein degradability has led to a new protein system called the metabolizable protein (MP) system. In this system, you balance to meet the requirements of the microbes and the animal, paying attention to the DIP and UIP fractions of the feed.

CP – Crude Protein: is the total amount of protein present as calculated from the total nitrogen present. Unless otherwise stated, protein values given in lab reports, feed tables and feed tags are crude protein. Laboratory analysis measures the total amount of nitrogen present in a feed. The per cent nitrogen is converted to per cent protein by multiplying by 6.25.

Source: Alberta – Agriculture, Food and Rural Development



Today, microalgae marketed as health food or food supplement are commonly sold in the form of tablets, capsules and liquids (Becker, 2004). However, there is always a long way for a new microalgae potential supplement from the Petri dish to the market place. The most relevant entity in food supplement regulation is FDA - Food and Drug Administration, of United States. In Europe the most relevant entity is EFSA - European Food Safety Authority.

Two products have already been approved as new dietary supplements: the natural carotenoid astaxanthin (produced by the microalgal specie Haematococcus) and the microalgal specie Arthrospira (Spirulina). 

Astaxanthin, unlike some carotenoids, does not convert to Vitamin A (retinol) in the human body. Too much Vitamin A is toxic for a human, but astaxanthin is not. However, it is a powerful antioxidant, and it is claimed to be 10 times more capable than other carotenoids (Mortensen and Skibsted, 1997). Haematococcus algae meal has been approved in Japan as a natural red food colour and as a pigment for fish feed. The U.S. Food and Drug Administration (FDA) approved astaxanthin as a food coloring (or color additive) for specific uses in animal and fish foods (see FDA have granted approval for Haematococcus algae to be used as a pigment in salmonid feed, and cleared for marketing as a dietary supplement ingredient. In the European Union, astaxanthin containing food supplements, derived from sources which have no history of use as a source of food in Europe, fall under the remit of the Novel Food legislation, EC (No.) 258/97. Since 1997, there have been five novel food applications concerning products which contain astaxanthin extracted from these novel sources. In each case, these applications have been simplified or substantial equivalence applications, because astaxanthin itself is recognised as a food component in the EU diet.


Spirulina contains an unusually high amount of protein, up to 65% by dry weight, and is a complete protein, containing all essential amino acids, along with good amounts of essential fatty acids, polysaccharide, phycobiliproteins, carotenoids, vitamins (especially B12), and minerals, making it a desired food source (Hu, 2004). In 2003, a notice was submitted by Cyanotech Corporation and Earthrise Nutritionals to FDA, for approval of dried biomass of Arthrospira platensis (Spirulina) as GRAS (Substances Generally Recognized as Safe). The response was: “Based on the information provided ... the agency has no questions at this time regarding the notifiers conclusion that Spirulina is GRAS under the intended conditions of use. ... As always, it is the continuing responsibility of the notifiers to ensure that food ingredients that the firms markets are safe... In particular, we note that any use of spirulina that constitutes use as a colour additive requires premarket review and approval by FDA.”. This issue is still in discussion between FDA and European Commission (see

The fact that some microalgal products are approved as dietary supplements does not mean that the same product from a new company is automatically approved. Actually, FDA states that “The fact that a new dietary ingredient is listed ... does not constitute a finding by FDA that it is not adulterated... (and) does not mean that another manufacturer can lawfully market the dietary ingredient in a dietary supplement.”

Regarding feed compounds market, EABA - European Algae Biomass Association is currently dealing with the legal procedures for approval of algal biomass as a feed material, covering the entire biomass incorporation and extracted algal nutrients incorporation.


Safety and International Standards

The most relevant entity establishing feed safety international standards is IFIF - International Feed Industry Federation. Compound feed production is dominated by the world's Big 4 - they are the USA, European Union, China and Brazil. These four countries account for more that 70 percent of all feed produced. They play a major role in standard setting and in the development of technologies used in our industry. Their feed organisations are members of IFIF:

FEFAC – European Union
CFIA – China
Sindirações – Brazil

Source: IFIF

Available data on Feed Standards by the referred organisations



Becker EW. 2004. Microalgae in human and animal nutrition. In: Richmond A., editor. Handbook of Microalgae Culture. Biotechnology and Applied Phycology. Oxford: Blackwell Science. 

Coffey, R. 2008. Digestive physiology of farm animals. Introduction to Animals and Food Sciences. University of Kentucky. Article

Cysewski G.R., Lorenz R.T. 2004. Industrial production of microalgal cell-mass and secondary products – species of high potential: Haematococcus. In: Richmond A., editor. Handbook of Microalgae Culture. Biotechnology and Applied Phycology. Oxford: Blackwell Science.

Firman J. 1984. Nutrient Requirements of Chickens and Turkeys. University of Missouri. Department of Animal Sciences. Article

Freeman, S. 2003. Biological Science. Prentice Hall. Article

Goodband R, Tokach M, Dritz S, Nelssen J. 1997. The Kansas Swine Nutrition Guide. Kansas State University - Agricultural Experiment Station and Cooperative Extension Service. Article

Hu Q. 2004. Industrial production of microalgal cell-mass and secondary products – major industrial species: Arthrospira (Spirulina) platensis. In: Richmond A., editor. Handbook of Microalgae Culture. Biotechnology and Applied Phycology. Oxford: Blackwell Science. 

McDonald P, Edwards R, Grenhalgh J, Morgan C. 2002. Animal Nutrition. Prentice Hall. Article

Merchen N, Titgemeyer E. 1992. Manipulation of amino acid supply to the growing ruminant. Department of Animal Sciences, University of Illinois. Journal of Animal Science 70: 3238-324. Article

Mortensen A., Skibsted L. H. 1997. Importance of carotenoid structure in radical scavenging reactions. J. Agric. Food Chem. 1997, 45 (8): 2970−2977. Article

NRC – National Research Council. 2001. Nutrient Requirements of Dairy Cattle. 7th revised edition. National Academy Press. Washington. Article

NRC – National Research Council. 1993. Nutrient Requirements of Fish. National Academy Press. Washington. Article

NRC – National Research Council. 1985. Nutrient Requirements of Dogs. National Academy Press. Washington. Article

Wondra K, Hancock J, Behnke K and Stark C. 1995. Effects of mill type and particle size uniformity on growth performance, nutrient digestibility, and stomach morphology in finishing pigs. Department of Animal Sciences and Industry. Kansas State University. Article


For more information on the nutrients description please see: