Fundamentals of Animal Nutrition
The health and viability of an animal depend on an adequate supply of nutrients i.e., substances like carbohydrates, fats and proteins that an animal body utilises as sources of energy or as parts of its metabolic machinery.
One of the essential properties of all living organisms is the metabolism - the process of absorbing, converting and secreting various compounds. If the metabolism breaks down all other bodily activities will soon come to a standstill. A very important task of the metabolic machinery is to provide sufficient energy. Carbohydrates and fats are the most important sources of energy, with the protein components, amino acids, only being used as a source of energy if present in excess of that needed for their specific functions or in the case of a deficiency of calories from carbohydrate and/or fat.
The quantity of energy a body needs is divided into the amount required for maintenance living, that is circulation, respiration, digestion, etc., and the amount needed for performance - growth, vigorous physical activity, work, and reproduction. It is vital, therefore, that an animal receives sufficient energy-yielding nutrients to cover its total energy requirements.
If we consider the animal organism as a metabolic machine, however, whose chief function is to break down organic food substances into molecules to manufacture its own "parts" and/or obtain energy, we soon realise how important and essential the catalytic and regulating mechanism is to the operation of the machine. This mechanism consists of enzymes and their cofactors, which may be "active" substances and/or "accessory food factors". These enzyme systems do not supply energy to the body but are essential for the transformation of energy and to the structure and regulation of the metabolic machine. Sometimes only traces of these factors are necessary, but all are essential to the organism and without which normal bodily activities would break down.
Following essential substances are important in a well-balanced diet:
We at NEKTON assure you that the very latest results of scientific research and an up-to-date knowledge of the various aspects of animal nutrition have gone into the development of all our products. Used correctly they will help you give your pet the best possible protection against deficiency illness or diseases.
We will look at some of the groups of effective substances or nutrients and their funtions or effect on the organism of an animal in detail on the following pages.
Vitamins are complex organic compounds essential in small quantities for normal growth, maintenance and reprodution of animal life.
Animals are unable to synthesise many of these compounds and they must obtain them "ready-made" directly or indirectly from the diet.
Until the turn of the twentieth century, nutritionists and lay people alike considered carbohydrates, fats, protein plus certain minerals to be the only dietary elements required for the normal functioning of the animal body. After animals became ill on a diet solely of the above nutrients supplemented with mineral elements, however, it became evident that natural foods must contain other substances in the diet indispensable for health, and a deficiency of one or more of these substances in the diet would result in a breakdown of bodily activities and produce symptoms of disease. This substances were first called "accessory food factors", later to be re-named "vitamine" (vitamins) by C. Funk of Poland.
Since their discovery, researchers have been able to isolate, purify, synthesise and elucidate the physiological action of many of these compounds. By 1913 only two vitamins had been discovered; one was fat soluble and the other was water soluble, so it was proposed to name them "fat-soluble A" and "water-soluble B". Classification by solubility in water or fat is still in use.
Nearly all normal. mixed diets will include sufficient amounts of vitamins and an avitaminosis (complete lack of one vitamin) is only likely to occur when a diet consists of only one kind of food.
Each vitamin influences a number of vital processes in the body and even a shortage eventually leads to irregularities in the metabolism and the functions of some tissues. Such a deficiency disease is called a hypovitaminosis and reveals itself in such symptoms as excessive fatigue and weakness, growth, retardation, reduced resistance to diseases, disturbances in reproduction and low resistance to parasites.
If there is a shortage of only one vitamin in a diet the hypovitaminosis due to this vitamin is usually recognisable by the symptoms and provided there is no irreversible damage, which, unfortunately, is often the case in a vitamin D deficiency, the disease can be cured by administering the appropriate vitamin supplement. Should a diet be insufficient in more than one vitamin, however, it is very difficult to diagnose a hypovitaminosis, as the symptoms are generally many and varied.
Frequently a pet owner does not always recognise or recognise in time that a diet is deficient in a vitamin, as the animal's organism may still hold reserves of this vitamin so that the symptoms of the deficiency disease are delayed or only slight at first.
to a vitamin deficiency:
As already mentioned, if the hypovitaminosis has not resulted in any irreparable damage to an animal's health, it can generally be cured quickly by the administration of a good vitamin supplement.
A hypervitaminosis, which is a disease resulting from an overdose of a vitamin, is even easier and faster to remedy. A hypervitaminosis is really only possible through the vitamins A and D and then only when the animal has ingested excessive amounts of one of these vitamins through an unbalanced and incorrect diet. It takes a hundred to a thousand times the recommended daily dose to produce a hypervitaminosis.
As scientists established the proper relationship between the nutrients of which food is composed, they discovered that a scant but well-balanced diet is infinitely superior to a lavish but unbalanced one. This is particularly true of the vitamins. Not only must the correct amount of each vitamin be present in the diet, but they must also be in the correct relationship to one another. A shortage of one vitamin cannot be compensated by increased amounts of the others. The vitamins are interrelated and the biosynthesis of vitamin C requires biotin, for example, or a vitamin B6 deficiency reduces the absorption of vitamin B12 in the gut as another.
A good vitamin supplement must therefore contain the right vitamins for its purpose and in the correct amounts and proper relationship. Years of research and experiments on their own animals have enable NEKTON to produce this excellent range of well-balanced pet diets and vitamin and mineral supplements. In addition NEKTON use only the very best forms of vitamins in their products. Special processing methods produce the pure vitamins in water-soluble powder form, meaning the products are easy to administer because of their water solubility and the vitamins remain active longer and better.
We will now describe each vitamin in detail.
Vitamin A is also known as the anti-infective vitamin as it protects the tissues of the epithelial cells of the respiratory, alimentary and genito-urinary tracts enabling them to maintain their ability to secrete mucus and thus their resistance to infection.
One of vitamin A's most important physiological functions is the maintenance of the visual sense organs. Insufficient vitamin A in the diet interferes with the regeneration of visual purple in the eye, causing night blindness, and leads to degenerative changes in the eye epithelium - the eye "dries out".
Vitamin A is stored in the liver but the liver of young animals is less able to store it that the adults' can. A vitamin A deficiency in the diet, therefore, leads to illness and disease in the young faster than in adult animals. Specific vitamin A deficiency symptoms in young animals are retarded growth and low resistance to infective organisms. Due to the loss of the epithelial cells' ability to secrete mucus the respiratory and alimentary tracts are usually affected first, resulting in pneumonia and diarrhoea. A classic vitamin-A-deficiency is choanal in amazons (oral area will show thickening and may shut due to swelling).
Provitamin A (Beta-Carotene)
The provitamin beta-carotene is found in the green parts of plants in a concentration of 10-200 mg/kilo and carrots have a particularly high concentration of this substance.
Carotenoids originate exclusively in plant material. The oxidisation of carotenoids produces xanthophyll and zeaxanthin, which are frequently used as natural colourings, e.g., when feeding laying hens to give the egg yolk a better yellow colour or to enhance the plumage of cage birds.
Carotenoids are found everywhere in nature and produce the yellow to red shades in plants and animals. They occur in blossoms, greens, corn, tomatoes, carrots, oranges, in the plumage of such birds as flamingos, and in fish and crustaceans.
Today carotenoids can be produced synthetically and are identical to the natural substances. An animal's organism processes and absorbs them in exactly the same way, whether the source is natural or synthetic.
Vitamin D (D2 Ergocalciferol, D3 Cholecalciferol)
Vitamin D's most important function is in regulating the calcium and phosphorus metabolism. Vitamin D2 and vitamin D3 are almost equally valuable in their antirachitic effect on mammals, whereas chicks and poults can efficiently utilise only vitamin D3. As vitamin D3 can also be stored better in the liver, NEKTON use only vitamin D3 in the manufacture of their products.
Vitamin D is required for the normal calcification of the growing bone and promotes the calcification of the eggshells of birds as well as maintaining blood plasma calcium and phosphorus levels and aiding calcium absorbtion from the intestine.
Many factors, the length of time an animal spends in the sunshine; its living habits and intake of calcium and phosphorus, all affect its dietary requirements.
Over a long period of time a deficiency of vitamin D in the young will lead to retarded growth and rickets, and to osteomalacia (lack of mineralised bone) in the adult animal, especially during reproduction and lactation.
Vitamin E (Tocopherol)
Vitamin E plays a vital role in all the body cells and in the fertility of most animal species. It also protects the vitamins A and C, vitamin A being conserved by vitamin E in chicks, for example, and its absorption or utilisation aided, meaning birds require a somewhat greater supply of vitamin E than mammals.
Vitamin E maintains normal muscle metabolism and ensures good functioning of the central nervous system and vascular system.
A vitamin E deficiency can lead to myocardial degeneration and degenerative changes in the skeletal tissues, reproductive tissues, liver and red blood cell membranes. Animals suffering from a deficiency of this substance are generally susceptible to infectious diseases. It is very important to ensure an adequate supply of vitamin E at all times, as any damage to organs due to a deficiency is usually irreversible.
Vitamin K (K1 Phylloquinone, K2 Menaquinone, K3 Menadione)
Alfalfa is an especially rich source of vitamin K1, which also occurs in lesser quantities in dark, leafy vegetables. K2 results as a synthesis by micro-organisms, particularly by bacteria living in the intestinal tract. The synthetic compound menadione (methyl-naphthoquinone), soluble in water, is even more active than vitamin K1.
These three forms, all possessing almost the same biological effect, are converted into active vitamin K by the body.
Vitamin K controls the synthesis in the liver of prothrombin and other blood-clotting factors to such an extent that a vitamn K deficiency reduces blood coagulation and leads to heavy haemorrhaging, especially in birds. This is the reason vitamin K is also given the name antihaemorrhagic vitamin or coagulation vitamin. Treatment with antibiotics and sulpha drugs are factors affecting the availability of vitamin K, as both prevent the correct synthesis of this vitamin by the intestinal flora. Birds have such a short intestinal tract and so few micro-organisms that they require a dietary source of vitamin K. This supply should be increased when they are receiving medical treatment as above or when breeding, as the vitamin K storage in the liver of newly hatched chicks is very small if not enough has been secreted into the eggs.
Vitamin C (Ascorbic acid)
Except for the primates (including Man), guinea pigs and deer, almost all animals are capable of forming vitamin C themselves from glucose. Today nearly all standard mixed diets will include adequate amounts of vitamin C so that deficiency diseases due to a lack of this vitamin seldom arise. An extra supply, however, will always be beneficial to an animal, and any surplus vitamin C is passed out of the body with the urine. As the body utilises larger-than-normal amounts of vitamin C in such stress situations as during illness, transport, etc., and the liver (in mammals) and the kidneys (in birds) cannot store more than very limited quantities of this vitamin, no balanced vitamin supplement should be without it.
Vitamin B Complex
Treatment with antibiotics and sulphonamides can destroy or reduce the availability of the B complex, which means that an animal's diet should be generously supplemented with these vitamins at such times to ensure maintenance of the bodily activities.
Most members of the group are poorly stored and very often destroyed by cooking. In addition, absorption from the intestinal tract is generally insufficient for a captive or domesticated animal's need, except in sheep, cattle and some in horses, meaning the food for such animals should be supplemented with the B vitamins to prevent a hypovitaminosis.
Vitamin B1 (Thiamine)
Vitamin B1, is also known as the antineuritic factor because of its physiological function in nerve activity.
A good digestive system and the carbohydrate metabolism depend greatly on sufficient vitamin B1. That means the richer the food is in carbohydrates the higher the vitamin B1 content in the diet must be.
General deficiency symptoms are fatigue, weakness and anorexia, resulting in weight loss and retarded growth as well as neurological disturbances and circulatory and cardiac involvement.
The supply of vitamin B1 should be increased in situations requiring a faster metabolism such as pregnancy, brooding or illness. In the case of gastro-intestinal diseases, which are often a factor affecting the availability of thiamine as they reduce absorption by the intestinal wall, the diet should also be enriched.
Vitamin B2 (Riboflavin)
Riboflavin is absorbed from the small intestine. A lack of vitamin B2 results in a number of different symptoms making it very difficult to diagnose. A distinct sign of a vitamin B2 deficiency in birds is severely turned-inward toes, commonly referred to as curled toe paralysis. Further symptoms are digestive disturbances, wasting, retarded growth, diarrhoea, poor hatchability and poor egg production, formation of crusty, horn-like material in the bill and small, weak babies.
Breeding birds should always have a good supply of vitamin B2 as a low riboflavin content in the eggs can mean death for the embryos and will certainly result in small babies susceptible to disease and of slow growth.
Vitamin B6 (Pyridoxine)
Vitamin B6 helps build proteins and is essential to carbohydrate metabolism. It is needed for the biosynthesis of unsaturated fatty acids, and a deficiency can result in a loss of weight. The numerous symptoms which a vitamin B6 deficiency can produce, such as a standstill in growth, over-excitability, muscle contractions, neurological disorders of the head and neck muscles, as well as those mentioned above show how essential this vitamin is for the normal bodily activities.
As vitamin B6 in the pyridoxine form is more effective biologically for birds than pyridoxamine or pyridoxal, this form is used in all NEKTON products.
Vitamin B12 (Cyanocobalamin)
Vitamin B12 has a decisive influence on all the metabolic processes and as it helps build proteins, too, diets poor in protein or fatty diets can still give full nutritive value if a vitamin supplement containing this vitamin is added. Vitamin B12 is used to treat pernicious and other forms of anaemia. Diseases and symptoms caused by a lack of vitamin B12 are an abnormal blood count, skin diseases, inflamed mucous membranes and uncoordinated movement.
Bird breeders should always ensure that their breeding birds have an adequate supply of vitamin B12, as a lack can cause the hatchability to sink to under 50%, and new-born birds are frequently deformed and display fatty degeneration of the liver, kidneys and heart.
Biotin (Vitamin H)
Biotin acts as a coenzyme and is involved in protein synthesis as well as carbohydrate metabolism.
Characteristic symptoms of a biotin deficiency are changes in the skin, a rough coat and loss of hair. Crusty scabs between a bird's toes and horn-like material on its bill or beak as well as sores can appear. Dogs often show neurological disorders if biotin is lacking in their diets.
Almost all the vitamins in the vitamin B complex, including folic acid, are necessary to ensure healthy growth, and a lack of folic acid can lead to rough plumage, loss of hair, and disturbances in the propagation. Bird breeders often find that a folic acid deficiency can lead to poor hatching results after only 5 - 6 weeks.
Nicotinamide / Nicotinic acid (Niacin)
Nicotinic acid is sometimes known as vitamin PP, the abbreviation PP standing for Pellagra Preventive, as a lack of this vitamin can lead to this skin disease in Man, which can be fatal when untreated. A niacin deficiency is characterised by dermatitis, loss of weight, retarded, diarrhoea and disorders of the central nervous system. A deficiency of this vitamin in dogs can lead to blacktongue i.e., increased deposits of melanine in the mucous membranes of the tongue. High corn diets can cause a niacin deficiency due to a tryptophan deficiency in corn protein and the low availability of niacin in corn. Leg disorders, slipped tendons or perosis are frequently observed in birds whose diets contain too little niacin.
A pantothenic acid deficiency leads to skin and hair lesions, gastro-intestinal troubles, retards the development of feathers and embryos and causes dermatitis in the area of the eyes, mouth, vent and feet in chicks. In some species a deficiency causes anaemia and general debility leading to reduced resistance to infection and parasites.
As pantothenic acid is required for the synthesis of cortical hormones, a deficiency may lead to necrosis of the adrenal cortex. It is essential that breeding birds receive enough of this vitamin at the very beginning of breeding as a deficiency can result in dead embryos or weak chicks.
Fully-grown animals can generally form enough myo-inositol for their needs from their normal diet. During growth, however, animals should be given an extra supply as they are unable to produce enough themselves.
Myo-inositol is found in most plant and animal tissues with grain heading the list of foods rich in this vitamin; which is the reason that poultry and other seed-eating birds rarely suffer from myo-inositol deficiency diseases. Myo-inositol is essential for growth and acts as a carrier for fatty acids. A lack of myo-inositol can lead to disturbances in the propagation, loss of hair and fatty degeneration of the liver.
Macrolements together account for 3.45% of body weight and each is present in the body at a ratio of at least 50mg to one kilo body weight. Microelements, on the other hand, or as their other name "trace elements" shows, appear in minute quantities in the body, that is, considerably less than 50mg per kilo body weight.
The essential mineral elements are as follows:
The above elements are essential to the structure and/or operation of the metabolic machine and must be present in fairly constant concentration in the healthy tissues of all living animals.
Consequently, all animal lovers whether breeders, collectors or pet owners must ensure that this concentration remains constant. An animal's organism is in a position to store many of these elements; the bones, for example, serve as temporary storage sites for calcium, phosphorus and magnesium. These reserves can be mobilised in times of stress for example or in the case of restricted dietary intake. If this dietary deficiency persists, however, vital body processes will suffer and eventually structural and physiological abnormalities will occur. In addition, the rate at which these elements are excreted by the various tissues and organs not only differs but also fluctuates, so that all in all it is the primary job of the animal owner to provide a dietary supply of these elements regularly. It may not always be possible to ensure that the supply meets all the body requirements at a particular time, but provided the dietary intake of the essential mineral elements is regular, the storage sites can usually meet temporary demand.
Now to the individual elements.
Ca and Phosphorus P
Calcium ions are principally absorbed in the proximal (upper and middle) part of the small intestine, and their absorption can be enhanced by ensuring an adequate supply of vitamin D in the diet at the same time. The excretion of calcium takes place via the large intestine and the kidneys, and the amount excreted fluctuates strongly. The dietary calcium in growing animals, for example, may be very high but the proportion of calium excreted extremely low as the calcium absorbed is needed for the skeletal development.
Phosphorus is absorbed mainly in the lower part of the small intestine. As in the case of calcium, it is difficult to assess the actual amount absorbed because it can be affected by a number of factors. It has been proved, however, that the intake of vitamin D and the correct ratio of calcium to phosphorus both improve its absorption.
Calcium's main function consists of forming bones and teeth and, in the case of birds, the additional calcium needed for egg shell formation. Calcium is also present in soft tissues where it carries out a number of regulatory functions in the body such as stimulating muscle contractions, making it important to the work of the heart. The greatest concentration of calcium not in the bones and teeth is found in the blood. All of the larger animals have 10mg of calcium per 100ml of serum. The vital minimum level of calcium in the serum is not regulated by the amount of calcium ingested, but is mobilised from the bones, which act as a calcium reserve.
In addition to the role of phosphorus in bone formation, it also plays a primary part in the carbohydrate metabolism, is active in fat metabolism and other life processes, and is the very core of the energy transmission system of the metabolic machine.
Because of the close relationship between the calcium and phosphate metabolisms, the ratio of calcium to phosphorus in the diet is of extreme importance, particularly for normal calcification of the bone and for reproduction. For most species of mammals the satisfactory range lies between 1.2 - 1.5:1, but the supreme calcium-to-phosphorus ratio for birds is regarded as 1.6 - 2:1.
Osteomalacia, rickets and a high incidence of bone fractures can all be the result of a calcium deficiency, which can also lead to heart and circulatory troubles. A deficiency of phosphorus in the diet can produce diarrhoea and loss of weight even when the daily food intake itself is high. Another deficiency symptom is reduced fertility.
A normal blood count depends on magnesium to a great extent, for 100ml blood serum contains 1 - 3mg of magnesium. Diets extremely low in magnesium will cause hyperirritability, tetany, muscle twitching and reduced blood pressure.
Magnesium is absorbed from the small intestine and is excreted in both the faeces and urine.
Na, Potassium K, and Chlorine Cl
Potassium and sodium are absorbed primarily from the small intestine, but apparently some absorption of the latter also takes place from the stomach. Chlorine is absorbed chiefly from the small intestine. All three elements are mainly excreted via the kidneys.
The main functions of the sodium ion in the animal body appear to be connected with the regulation of osmotic pressure (the pressure against a membrane between a concentrated and a less concentrated liquid) and the maintenance of acid-base balance, although together with potassium and chlorine it plays an important role in water metabolism as well. Potassium also regulates the osmotic pressures and the acid-base balance but from within the cells, whereas sodium carries out these functions in the extracellular fluids of the body.
Close relationship exists between chlorine and sodium, too, both of which are found in the extracellular fluids, and therefore both are responsible for the regulation of the osmotic pressure outside the cell. Chlorine constitutes about two-thirds of the total anions of blood plasma.
The interrelationship between these three elements becomes clear when we see that excess chloride retards growth if it is not compensated by sodium and potassium, and vice versa.
A sodium deficiency will adversely affect appetite and normal increase in weight and cause low blood pressure, rough coat and cardiac troubles.
The abundance of potassium in both plant and animal foods normally precludes the danger of a deficiency in this element. In fact, the healthy balance between sodium and potassium in the body is often upset by excess potassium, which can only be regulated by an increased intake of water and sodium.
A chloride deficiency can retard growth as well as adversely affect viscosity and nerve impulses.
Because of their terrible taste and because they act as a laxative, e.g., Glauber's salt or Epsom salt, animals are not partial to the fast soluble sulphates, sodium or magnesium sulphate. That is why the sulphur in today's diets or supplements is in the form of the sulphur-containing amino acids cysteine, cystine and methionine.
TRACE ELEMENTS (Microelements)
The absorption of iron is influenced by the state of the body's iron stores. Dietary iron is ionised by the stomach acids then passes into the cells of the intestinal lining, and the rate at which it is released from these cells into general circulation depends on how saturated with iron the blood protein transferrin is. The body's need for iron thus affects the absorption of the element from the gastrointestinal tract.
Absorbed iron is converted into haemoglobin and is therefore part of the process where oxygen is taken up from the air in the lungs and carried to the tissues. It contributes to the energy metabolism and aids resistance to infection. Anaemia is the well-known result of an iron deficiency, but a lack of this trace element can also lead to an increased susceptibility to infection and symptoms of toxicosis.
Copper and iron are sometimes considered together because of their joint importance in the formation of haemoglobin. Because of this relationship, anaemia can result from a copper deficiency as well as from an iron deficiency. A deficiency of copper decreases fertility in cattle and hatchability is reduced in birds. Embryonic abnormalities can occur in birds on a diet poor in copper.
Copper has an important function in hair growth, the formation of the melanin (dark) pigment of skin and hair, and the bone and connective tissue formation.
Due to poor absorption of manganese in the gastrointestinal tract and the low concentration of this trace element in the body tissues, great care must be taken to ensure a regular supply of manganese in the diet. A deficiency of this element frequently affects skeletal development, particularly in birds, and results in shortened and often deformed limbs. A low manganese diet can often lead to sterility in male mammals and late sexual maturity in females. As already mentioned, perosis in birds is the result of a lack of manganese in the food ration and should a choline, vitamin E and biotin deficiency arise at the same time an outbreak of this syndrome is unavoidable.
Zinc is important primarily for skeletal development and the formation and regeneration of the skin and hair cells. Symptoms of a deficiency, particularly in young animals, are bone deformation and retarded growth as well as impaired hatchability and poor feathering in birds.
A dietary insufficiency of iodine means an absence of sufficient thyroxin in the blood causing the thyroid to work harder to produce thyroxin and, in the process, enlarging it to what is called goitre. Goitre even occurs in the newborn, primarily as a result of insufficient iodine in the diet of the pregnant female. The thyroid hormone is essential for normal growth and reproduction in all mammals and birds, so that a deficiency leads to a depressed basal metabolic rate, disturbed propagation and stillborn babies.
The remaining essential microelements are:
C, Tin Sn, Vanadium V, Nickel Ni and Silicon Si
All these elements are essential in one way or another. Vanadium and chromium improve the growth rate of rats; silicon appears to be necessary for normal growth and skeletal development of chicks, tin likewise, and a nickel deficiency results in an inferior liver function. Practically all of them, however, have been shown to be toxic in comparatively slight overdoses.
Normally the metabolisable calories yielded by carbohydrates and fats supply the energy to keep the body warm and drive the processes of life, but in the case of a deficiency of calories from carbohydrates and/or fats part of the protein will be used for energy, too.
Although protein may serve as a source of energy, it is important primarily as a source of amino acids, substances used in making new protoplasm and cells and therefore essential for growth and replacement. An organism builds its own structural and functional proteins from the amino acids. Neither carbohydrates nor fat can fulfil this function, as neither contains the necessary element nitrogen.
Excess protein cannot be stored in the body like fats and carbohydrates, and as the body uses up protein all the time, a deficiency soon shows serious effects. Without a fresh supply the total body protein is reduced by half in about 80 days, for example, and the half-life period of liver protein is only 10 days.
This means first of all that enough protein must be supplied by the diet to replace the used body protein. As 70% - 75% of the dry matter in muscles is made up of proteins, and such tissues as hair, wool, feathers, nails, horns and hooves are largely protein in nature, an even greater supply is necessary at times of growth and muscle building because of the rapid protein consumption at these times. This means that baby and young animals automatically have a higher protein requirement than adult animals.
Up to now we have mainly spoken of protein and protein requirements, but for the nutritionist the most important factor of protein is its amino acid make-up. Every animal owner today knows that not all proteins are suitable for his particular species. This means that the value or quality of the diet should not be judged on the amount of protein in the food but on the amino acids it contains. Animal protein usually contains a higher concentration of the essential amino aicds than plant protein.
The proteins in the diet are broken down into amino acids by the enzymes in the stomach, duodenum and ileum (small intestine) and as such soluble compounds pass through the intestinal lining into the blood stream where they are carried to the cells to be turned into body protein.
Proteins are made up of one or more chains of amino acids.
The following table shows over 20 of the 20 - 25 known amino acids.
Not all the amino acids listed above are necessary as dietary components as some can be synthesised in the body from a suitable carbon source and amino groups from other amino acids. These are called dispensable or non-essential amino acids, but this only means they are dispensable in the diet and not to the animal. Indispensable = essential amino aicds are those that cannot be synthesised in the body fast enough to meet the physiological needs of the body or cannot by synthesised at all by the body and must therefore be furnished preformed in the diet.
A well-balanced diet must contain high-quality proteins supplying an abundance of the various indispensable amino acids.
As already mentioned, there are 20 - 25 different amino acids in existence, and the particular way they are combined in each protein determines its bio-chemical characterisitics, but the amounts of the various amino acids present in a protein determine its nutritional value. The nutritive value of a particular protein, however, must be considered in relation to all the other proteins in the diet, because although a protein can consist of 50 - 5000 different amino acid combinations, it is seldom the case that a single isolated protein contains all the essential amino acids needed by a certain species and in the right balance. The proteins of cereal grains, for example, are likely to be deficient in lysine and threonine, whereas the proteins of seeds of legumes, such as soybeans, are relatively well supplied with lysine and threonine but lack the sulphur-containing amino acids such as methionine and cystine. If just one of these amino acids is missing or under the requirement level the body cannot make its own body protein. Even if the others are present in excess of requirements, the "chain" is incomplete and this one amino acid would limit protein utilisation. In such a case we call this the limiting amino acid.
An apparently satisfactory level and balance of amino acids in dietary protein does not always guarantee, however, that ingestion of the diet will satisfy the amino acid requirements of an animal. Under certain conditions some amino acids may by unavailable because the proteins in the diet are incompletely digested or the construction of the plant cell walls also renders the proteins in the cell inaccessible to the digestive enzymes. The presence of inhibitors of the digestive enzymes, such as the trypsin inhibitor in soybeans, may impair the digestion in some cases and, of course, illness or medical reatment can reduce the amino acids' availability in others.
With all this attention to the amount, quality and type of protein needed as a source of amino acids in the diet, we must not forget the three different, interrelated metabolic pathways amino acids may follow within the body: (1) used for protein synthesis; (2) serving as precursors in the synthesis of such nitrogen-containing compounds as choline and thyroxine; (3) as a source of energy. Balance among these pathways is constantly regulated so that changes in the rate of disposal along one route are compensated by changes along one or both of the other pathways. This means that in our efforts to provide a diet well-balanced in protein we must not forget to provide a supply of carbohydrates and fats in ratio to the protein, for a sub-optimum in calorie/protein ratios results in the degradation of amino acids to meet the energy needs of the body, whereas calorie/protein ratios much higher than the optimum result in an inadequate intake of protein.
Thus the protein nutrition is a somewhat complicated subject, and there is a lot more to be said about it. We would just like to point out that over 90% of the protein in our products is already in its digested form, amino acids, and in the natural L-form, the only form the body can use. This means it can start fulfilling its different functions in maintenance, growth, reproduction and as an energy source for the body at once, without the strain of digesting.