See also signs of illness.
Metabolism may be described simply as the utilization of food and its effects within the body. These include the building up (anabolism) and breaking down (katabolism) of the chemical substances from which the body is made. The processes vary from species to species depending upon inherited bio-chemical characteristics and also upon individual variations, which include age and activity as well as environmental factors such as diet and exposure to heat or cold.

This group covers those diseases where the chemistry of the body has been disturbed. Sometimes we can explain how and where the mechanism has gone wrong, but we can rarely explain why. There is no obvious cause---such as an invasion by bacteria or other infectious agent. In a proportion of cases it is possible to trace the trouble back to a derangement of the hormone production of the ductless glands. As explained these hormones or so-called chemical messengers modify the rate and type of activity of many of the basic chemical reactions necessary for the life of each body cell and of the body as a whole. When hormones are produced in too small or excessive amounts, the body's complicated reactions cease to work properly. Some of these disorders happen for no apparent reason, while others come about as the result of too much stress being placed on a particular system of the body. At first the organism takes the strain and gets along normally for a while. Eventually, however, illness in some form results. The stress may be starvation, unsuitable food, exhaustion, inactivity, fear or exposure to extremes of temperature. Sometimes a gland may be directly damaged by injury, or it may be replaced by tumor cells. The change of tissue cells from normal to those of a cancerous type could even be said to be a metabolic disorder; but since this tends to complicate an understanding of metabolic disorders, tumors are dealt with elsewhere.

The relationship of carbohydrates to disease is threefold. Carbohydrates (which include starches, sugars and cellulose) may be actually deficient in the diet. This is extremely rare in the average range of avian diets except when the bird is starved, fed grossly abnormal foods, or is completely off nourishment for some reason. Carbohydrates may be inadequately metabolized due to lack of certain vitamins, an excess of indigestible fibrous food, mechanical interference with digestion, or pancreatic disease affecting digestive processes. Thirdly, they may cause disease by virtue of their quantity being excessive in the diet in relation to other essential foods.

Defects in carbohydrate metabolism are common even when the proportion and types of these foods are correct. Normal utilization depends first on absorption from the gut. If gut movement or secretions are abnormal, including those in the stomach and from the pancreas, regurgitation or diarrhea are liable to result. The causes are numerous and include vitamin deficiencies, infections, foreign bodies, exhaustion of the adrenal cortical tissue and some types of poisoning. In old age, spontaneous carbohydrate digestive disturbances arise especially when good quality protein is low in the diet. Excessive dietary intake of carbohydrates is not necessarily associated with overeating. Highly efficient digestion and absorption, with an impairment of the "overflow" mechanism of surplus food can lead to the accumulation of excessive amounts of body fat. Normally this is deposited in special fat depots designed for the purpose, under the skin, lining the body cavity, and so forth. In certain glandular dysfunction's and other disorders due to almost unknown causes, fat may be deposited practically anywhere in the body, such as in the connective tissues which hold the various organs together. This fatty infiltration is most noticeable in the highly active organs such as the liver, heart and kidneys, which it severely hampers.

Carbohydrates are the main and most readily available forms of energy. They are the so-called storage foods or starches, which form a large part of the normal diet and are found in high proportions in such foods as cereals, grains and fruit. Meat also has quite a high carbohydrate content. All carbohydrates contain atoms of carbon, hydrogen, and oxygen, combined together in chains or rings with various side branches. The structural units from which carbohydrates are formed are known as sugars. The simple 6-carbon sugars are called monosaccharides; the more complex ones such as lactose and sucrose are known as disaccharides, while the starches and cellulose with numerous molecules are termed polysaccharides.

Glycogen is manufactured by the liver, active organs and muscles and from simple carbohydrates or sugars. The glycogen is stored and can be mobilized by various nervous and chemical mechanisms at extremely short notice when a sudden flood of energy is needed.

Fats and Oils:
A lack of fats and especially oils tends to hinder the absorption of the fat-soluble vitamins A and E, and results in their deficiency even when they are present in the food. If fats in the diet are low, the carbohydrate and protein constituents also are not efficiently used. Although recognizable illness may not show itself, the bird tends to overeat, converting carbohydrate to body fat which has a damaging effect on tissues, particularly the arteries, and makes the bird sluggish. A high fat diet may upset the digestion, and tends to reduce the appetite; unless excessive, this produces a lean but active bird with a glossy plumage. Mineral oils such as liquid paraffin are not absorbed and in lubricating the alimentary tract they also remove valuable fat-soluble vitamins, these becoming excreted in the feces. Vitamins such as A and E are oxidized and damaged by substances in rancid oils. The oily seeds like linseed do not suffer from this rancidity, while still intact and fresh; but heat-treated pellets, dead stale gentles, and above all stale cod-liver oil are important causes of ill health from vitamin destruction. The chemicals which cause fat rancidity are themselves poisonous to birds.

Fats are a concentrated source of energy, but they are largely replaceable in this function by carbohydrates; some oils or unsaturated fats are, however, more chemically active and appear to be essential for growing chicks, if not for adult birds. Most seeds and nuts contain these "oily fats" and are therefore preferable to animal fats, except fish oils.

Fats and oils (unstable fats) consist of organic acids called fatty acids. They are also mainly composed of carbon, hydrogen, and oxygen. Fats are long term reserves of concentrated stored energy which also furnish heat insulation and some protection against injury. In addition, they help to maintain the health of skin and plumage and aid in the absorption of fat-soluble vitamins. When food is short, fats are utilized by the body. Fat is also a source of certain unsaturated fatty acids which are essential ingredients of the diet. An excessively high level of fat in the diet slows the emptying of the stomach and consequently the digestion of all food in the digestive tract. It is therefore wasteful and interferes with the utilization of other vital nourishment.

Proteins are long chains of smaller compounds, called amino-acids which contain carbon, hydrogen and oxygen plus nitrogen and occasionally sulphur. They are used in the formation of body tissue needed for growth, to replace proteins broken down in bodily functions, and to furnish the proteins required in making eggs. Proteins are also present in high proportion in most organs and tissues of the body, particularly feathers, skin and appendages, the heart, liver, kidney and eggs.

Protein is the third and last storehouse of energy. In starvation or prolonged disease, after most of the fat storage depots have been depleted, the body starts to use this only remaining material. Muscle wastage then becomes noticeable, particularly over the breast and limbs in birds. The protein breaks up by discarding its nitrogen-containing element and becomes a carbohydrate-like substance which can be readily utilized. Much of the nitrogen is excreted in urine. The resultant loss of weight in birds is spoken of as "going light".

In certain circumstances, for example when there is an imbalance of protein in the diet (especially of such psittacine birds as budgerigars and parrots), the metabolism becomes deranged and waste by-products accumulate in the body, producing gouty deposits near the joints of the limbs and in the internal organs. There are about twenty different types of amino-acids. Some of these can be manufactured by the bird, and therefore are called non-essential amino-acids. The other group, the essential amino-acids, cannot be manufactured by the bird and must be supplied in the food. Plant proteins tend to be deficient in certain essential amino-acids and therefore it is often desirable to add special protein supplements to the diet of seed-eating birds kept in captivity. In the wild state, such birds would eat a wide variety of invertebrates and also feed them to their young, thereby obtaining animal protein and the essential amino-acids.

The precise requirements of the different amino-acids for birds are unknown, even for poultry, and differ according to species. Tyrosine and lysine appear necessary for feather pigmentation, while the former is also used in the formation of the thyroid hormone, thyroxine.

Even when analysis of a foodstuff may show a reasonable proportion of protein, say 12-16 per cent, it does not necessarily mean that the protein it contains is of value to birds. Much vegetable protein is of poor quality because it contains insufficient amounts of the essential amino-acids. In fact, seeds commonly fed to cage birds, such as the millets and maize, are low in total protein and are also deficient in methionine, cysteine, tyrosine, and certain other amino-acids. Turkish hemp, niger seed, teazle, and some other so-called "tonic foods" are better in this respect. When poor quality protein foods are fed, health suffers according to the tissue most starved of amino-acid nourishment. Since glandular tissues, muscle and skin have high requirements of those amino-acids which contain sulphur, prolonged periods on a diet deficient in this way lead to hepatic and renal disease, poor breeding, scurfy skins, faded plumage and muscle weakness.

Excessive protein in the diet of grain-eating birds increases the requirements of vitamin B12, which may produce signs of vitamin B deficiency, especially in nestlings. Scavenging and meat- or fish-eating birds normally flourish on a diet containing 25-30 per cent good quality protein. Not only does their diet contain considerable amounts of B12, but their constitution is adapted to this high protein diet. The protein requirements of birds in general appear to be higher than those of mammals. The high requirements of breeding hens and nestling chicks are met by the parent providing much animal protein in the form of invertebrates such as insects or in the case of pigeons the special fluid known as crop-milk and a similar proventricular secretion in budgerigars. In captivity, a common source is egg food. A long-term result of both very high or very low amounts of protein in the diet is the deposition of gouty deposits through the body. This may be the result of stress and exhaustion of normal kidney tissue, toxicity of the amino-acid glycine, or damage to the kidneys by lack of the raw materials for their repair.

The term vitamin is applied to widely differing groups of chemical compounds which are essential to nutrition but do not necessarily bear any structural or functional relationship to each other. It is important to remember that nature provides an adequate amount of all vitamins--provided that a wide variety of fresh foods is eaten. When foods are stored for long periods, especially in damp containers, and are fed day after day with no variety, relative deficiencies of one or other vitamins can and do occur. Diets which are low in vitamins are often low in some of the essential amino-acids which make up good quality protein, and such complicating factors make the diagnosis of vitamin deficiencies difficult. Disease also increases the demand for vitamins and may interfere with their absorption or utilization. Freshly gathered natural foods such as leaves, fruit, or seeding grasses are a better and more balanced vitamin and mineral tonic than many commercial products.

Proprietary vitamin supplements should normally be necessary only for sick birds and those unable or unwilling to eat normal food. Single vitamin deficiencies rarely occur naturally and are the province of the experimental worker in avian diets who may create them to order, for research purposes. Unlike carbohydrates, fats, and proteins, vitamins are catalysts and are able to aid chemical processes and remain unchanged at their completion. In cage birds, vitamin requirements vary with species, and owing to their differing natural diets some birds are more likely to be affected than others.

Vitamin Deficiencies:
With one or two notable exceptions, there has been very little experimental work on vitamin deficiencies or imbalances in cage birds. Most of our knowledge is derived from information on the effects of deficiencies in the fowl, turkey, duck, or pigeon applied to similar symptoms in cage birds. This may not always lead to a clear understanding of such diseases, especially as single deficiencies or excesses rarely occur naturally.

Vitamin A:
Vitamin A is essential for growth, maintenance of a healthy skin and mucous membranes, and for good vision. A deficiency of the vitamin has an adverse effect on the epithelial lining membranes of the respiratory, alimentary and reproductive tracts and allows infections to gain ready entry to the body. It has sometimes been called the "anti-infective vitamin". It does not really protect or combat organisms trying to invade, but does assist the membranes to function normally, that is to act as a barrier to disease. Vitamin A is stored in the liver and is found only in animal tissue. Its precursor carotene is found in all green plants and yellow seeds and is converted by the body into vitamin A.

A deficiency of vitamin A has an adverse effect on the epithelial lining membranes of the respiratory, alimentary and reproductive tracts and allows infections to gain ready entry to the body, especially to the skin and mucous membranes. It has sometimes been called the "anti infection" vitamin. It does not really protect or combat organisms trying to invade, but does assist the membranes to function normally, that is to act as a barrier to disease.

Mucous membrane lines the mouth, nostrils, pharynx and the alimentary, respiratory, urinary and genital tracts. The tubular glands branching off from these tracts may become blocked by damaged cells and exudate, whilst the tubules of the kidney are also affected. It is not therefore surprising that lesions caused by vitamin A deficiency may be widespread. The clinical signs most commonly seen in young pigeons and some other birds, consist of rattling, respiratory sounds, and mucoid or purulent discharges from the eyes, nostrils, mouth, and even the vent. The discharges are partly made up of abnormally thickened, horny membrane and portions of dead cells thrown off the mucous membranes. If the inside of the mouth is examined, ulcers and cheesy, necrotic or diptheritic membranes can be seen, the latter occurring as soft, whitish, loose deposits which partially block the nostrils, throat or glottis. Beneath the eyelids and in the sinus below the eyes a thick, cheesy deposit sometimes builds up and causes a bulge in the overlying skin; these exudates are partly produced by bacteria which flourish in the damaged membranes. Other features of vitamin A deficiency are dullness of the plumage, weakness and poor appetite, and unsteadiness which suggests that even nerve function may be impaired. When a breeding female is deficient, the eggs she produces show a high incidence of dead-in-the-shell and weakly chicks. Post-mortem findings include pale kidneys and sometimes gouty deposits on several organs.

Lack of vitamin A is most likely to be confused with trichomoniasis, candidiasis (moniliasis), pox, and possibly aspergillosis, since all these show similar exudates in the upper respiratory and alimentary tracts. Treatment can be carried out by injections or oral dosing of vitamin A or by providing foods containing a high proportion of the vitamin. But since infections sometimes also play a part in severe deficiency, the use of broad-spectrum antibiotics may also be necessary. It is often preferable to destroy affected young birds because normal growth and development is seldom completed and they remain stunted and disease-prone. A clinical hypervitaminosis A (excess of vitamin A), does not appear to occur as a problem in birds.

Vitamin D:
A deficiency of this vitamin (see also Calcium and Phosphorus deficiency), which gives rise to bone problems in the young, should be suspected when chicks of any species develop weak legs with swollen joints. Affected birds are also stunted, and limb fractures may occur without any marked violence or accident having taken place. Deficient adult hens lay thin or soft-shelled eggs and the clutch size may be reduced. Leg weakness in adult birds, softening of the beaks and claws, fractures or bending of the bones, including caved-in ribs, denote vitamin D deficiency which is called osteomalacia, or adult rickets. Small knob-like swellings can also sometimes be felt on the ribs at the junction of the vertebral and sternal parts. Deficiencies of vitamin D2 and especially D3 in birds prevent absorption of calcium and phosphorus, both of which are essential in order to strengthen the bones and support the body.

A marked excess of vitamin D3 which can be reproduced by repeated administration of the vitamin in large amounts, rarely occurs. When it does, however, it is liable to cause kidney damage. Calcium salts become deposited in the walls of the kidney tubules and in the walls of blood vessels, especially the major arteries as they leave the heart. This syndrome has been seen in aged parrots and cockatoos although it is not possible to relate its occurrence to excess vitamin D3 in the diet. Treatment by administration of vitamin D3 in deficient birds is best carried out by injection, which is quicker than by giving it in the diet.

Vitamin D is required for the normal production and maintenance of bone, the absorption of calcium and phosphorus for making egg shells and also for maintaining the quality of beak and claws. The amount needed varies. Vitamin D promotes the retention of minerals by increasing absorption or decreasing their excretion. Sun-ripened seeds and leaves, eggs and fish liver oils are rich sources of vitamin D2. Vitamin D3 is the form available for birds, being found mainly in eggs and fish liver oils. Vitamin D is synthesized in the skin, especially the un-feathered parts, by the action of direct sunlight. It is also believed that the secretion of the preen gland is converted into the vitamin by the action of sunlight when it is spread on the feathers.

Vitamin E:
Vitamin E consists of a group of fat-soluble, unstable, organic compounds known as tocopherols, and is believed to have several far-reaching effects in the body, although even in man, domestic animals, and poultry, its functions are not dearly understood. In most birds it is probably needed for normal development of skeletal muscle, nerve cells of the brain, maintenance of protein levels in the blood, the health of male germ cell-producing tissue of the testes, and especially for the development and growth of embryos. The tocopherols are found in the germ oils of many seeds and in fresh green foods. The effects of the vitamin, however, are very easily negated through oxidation by unsaturated fatty acids in rancid oils and minerals. If cod liver oil is mixed with seed and stored this may happen. Administration of liquid paraffin or other oil prevents the absorption of vitamin E.

No reports of softening of the brain due to lack of this vitamin have been made in cage birds. It is also known as encephalomalacia and results in "crazy chick disease" in poultry. In foodstuffs, vitamin E protects oils and vitamin A against destruction by oxidation or rancidity, but in doing so is itself destroyed. There is therefore a constant danger of a deficiency of this vitamin when foods are fortified with cod liver oil. Deficiency of vitamin E seems to show itself differently in different species and includes wastage of muscle fibres, the encephalomalacia referred to above, exudation or dropsy of the tissues, and enlarged hocks. Adult birds do not often appear to suffer severe damage to the testes and reproductive powers as do some mammals, but this possibility should be borne in mind when confronted by problems of infertility and breeding. Although hens deficient in vitamin E continue to lay eggs, the embryonic development is impaired and embryos are liable to die early in the incubation period. Crippling hock enlargements are quite commonly seen in some cage-bird chicks, but whether any of these cases are due to deficiencies of vitamin E is uncertain. Provision of fresh natural foods, such as the germ of wheat and other grains and some green foods, is preferable to dosing with the vitamin when a deficiency is suspected.

Vitamin K
Vitamin K is necessary for clotting of the blood. It is present in most green leaves and grass. Bacteria of the lower intestine synthesize some vitamin K, but this is probably significant only in species where considerable fermentation occurs, e.g., in those seed-eaters which have well-developed caeca and colorecta. Deficiency rarely occurs but could result from indiscriminate use of antibiotics, especially if mixed in the food or water, when they are more likely to cause changes in the intestinal, bacterial flora and thus affect the synthesis of the vitamin.

Vitamin B Complex:
The Vitamin B Complex is a large group which contains several important and separate vitamins. Most play an important role in metabolism.

VITAMIN BI, THIAMINE OR ANEURINE, is a water-soluble compound, unstable in heat. It is important to all cells of the body, including nerve cells, since it is involved in the metabolism of carbohydrates; without it death soon occurs, preceded by severe nervous disorders. Cereal grains and their by-products usually contain a sufficiency of this vitamin, but certain seeds such as mustard, hot rape, and fresh fish, contain substances which destroy the vitamin.

VITAMIN B2, OR RIBOFLAVIN, is a heat-stable and water-soluble compound. It takes part in several chemical processes in the tissues involving the building up, normal function, and breakdown of cells, and the metabolism of oxygen and other gases carried by the blood. It is contained in most green foods, yeast, liver and milk.

VITAMIN B6, OR PYRIDOXINE, is a stable member of the vitamin B complex and is necessary in various chemical reactions concerned with the metabolism of proteins and fat. Requirements vary greatly between species, and even breeds, of birds. Since the vitamin is widespread in avian food-stuffs, it is unlikely that deficiencies of pyridoxine will occur.

VITAMIN B12, OR CYANOCO-BALAMIN, OR COBALAMIN, is water soluble. It has numerous functions in the metabolism of many food substances and chemicals of the body and is not produced by plants or animals above the most primitive forms of life, e.g., single-celled organisms and bacteria. Having the metal cobalt in its make up, it can be compared with the pigment chlorophyll of plants, which contains magnesium, and with the hemoglobin of vertebrates, which contains iron. The vitamin is absent from green plants and seeds but is found in meat, milk products and yeast. Although it is synthesized by intestinal micro-organisms a dietary source is also necessary. Deficiency is particularly likely to arise when the bulk of gut bacteria are killed by excessive administration of sulfonamides, antibiotics, or other antibacterial drugs.

Deficiency has deleterious effects on skin, feather and horn, and also retards growth, causes poor appetite, and reduces hatch-ability of eggs. The vitamin is often used as a tonic, to stimulate numerous body processes. Its part in feathering is related to the intake of methionine, choline, and folic acid, since methionine, for example, is an important sulphur-containing amino-acid essential for the production of several tissue proteins including those of feathers.

Pantothenic acid, which is easily destroyed by heat, plays an important part in the metabolism of the three main food constituents, carbohydrates, fats and proteins. Other functions include the production of acetyl choline, vitally important in the conduction of nerve impulses and in their translation into muscle movements and other functions under nervous control. There is evidence that in some birds the requirements for this vitamin depend to a large extent on the amount of vitamin B12 in the diet. Although seeds such as wheat and oats provide an adequate supply of pantothenic acid, the richest natural sources are yeast and liver.

Nicotinic acid and niacin are closely related compounds which are involved in the metabolism of the three main food constituents, but at a different stage from pantothenic acid. Some seeds such as maize (known in the U.S.A. as corn) and oats are relatively poor sources of these substances. Tryptophane is usually adequate in the diet.

Folic acid, which is fairly stable, plays a restricted but important part in the synthesis of certain body proteins and is also stated to be an anti-anemia factor. Seeds and grains are not generally rich in the vitamin, but yeast and liver will supply any deficiency in the normal diet.

Choline, like pantothenic acid, is essential for the formation of acetyl choline and is also involved in fat metabolism. The richest sources are yeast, liver, fish meal and fish solubles. The amount required in the diet is dependent on the vitamin B12 intake.

Biotin or vitamin H is stated to prevent perosis and poor hatch-ability, although no definite metabolic role has yet been established for the compound in birds. It is a complex sulphur-containing substance and occurs in many foodstuffs including yeast and milk by-products. Unheated egg white contains a protein which can react with biotin in the intestinal tract and thereby render it unavailable to the bird, thus producing a deficiency of the vitamin.

The vitamins in this group are so closely interdependent in their functions that it is customary to deal with them together. It is likely that if one is lacking, the others are also. Deficiencies of this complex can only be suspected with reasonable certainty when the symptoms are similar to those proved to be caused by deficiency in other birds and mammals, and when also the birds respond to treatment by restoring the suspected vitamin deficiency in the diet. Leg and wing weakness, clenched feet, "slipped-toe", curled toes and other evidence of neuromuscular disorders suggest aneurine (thiamine) or possibly riboflavin deficiency, especially in chicks; although there are many more likely alternative causes, such as arthritis or injury, and in adult budgerigars pressure from a renal tumor on the sciatic nerve. Other nervous signs such as tilting back of the head, weakness of the neck, violent tremors, convulsions, in-coordinated movements sometimes leading to coma and death, may signify a shortage of aneurine or pyridoxine or perhaps a folic acid deficiency.

In adults, such signs are often attributable to circulatory or respiratory disease, head injuries and brain tumors, or the terminal stages of some infectious diseases. Poor feathering, including stunted feather growth or loss of pigment in the feathers may be due to riboflavin, pantothenic acid, or folic acid deficiency; such causes, however, as French molt, protein deficiency, thyroid or pituitary disease must not be overlooked.

Dermatitis of the scaly parts of the legs and scabs on the head near the beak and on the eyelids are sometimes due to deficiencies of riboflavin, pantothenic acid, and biotin, as well as acute lack of vitamin A or oil. Deformities of the skeleton, especially the long bones of the limbs and beaks, and swollen hocks, make investigation into the diets of affected chicks and breeding hens worthwhile. Possible deficiencies include pantothenic acid, nicotinic acid, biotin, folic acid, and choline as well as vitamin D3 and minerals such as calcium and phosphorus. These are so closely interdependent in their actions that they will be considered together. Both minerals are essential to the diet and need to be present in the correct ratio.

The ideal ratio varies somewhat, not only according to the age of the bird and whether or not eggs are being produced, but also possibly according to the species. Generally speaking, however, the proportions of phosphorus to calcium should be between 1.5:1 and 3:1, provided that sufficient vitamin D is also supplied to assure absorption of the minerals. Most of the calcium in avian foods is absorbed. No common food is rich in this mineral, but green foods, especially clover, and animal foods supply a proportion of the requirements. The remainder comes from the soluble or shell grit, which is eaten in noticeably greater amounts by breeding birds. Phosphorus is abundant in the common cereal foods fed to birds, but a large part is in an unavailable form. Animal foods such as gentles contain much less, although it is mostly absorbable.

The bodies of all warm-blooded animals include metallic elements in addition to the organic chemicals, which always contain carbon, hydrogen, oxygen, nitrogen and water. These elements, in combination with their salts, are referred to as "ash" in analyses and represent the un-burnable parts of the body. This ash consists of a high proportion of dehydrated tissues and contains calcium (as the phosphate and carbonate), sodium (as the chloride), magnesium, potassium, and much smaller amounts of iron, copper, sulphur, iodine, manganese, fluorine, zinc, cobalt, molybdenum, and selenium. Such minerals are called trace elements, and although minute and measured in parts per million as opposed to percentages of the total body weight, are nevertheless essential to normal development and health. Minerals enter into the composition of bone and give the skeleton rigidity and strength to support the soft tissues. They also combine with protein and other substances and help to form the body tissues. Other tasks include a role in the functioning of protoplasm, the transport of oxygen and the maintenance of degrees of acidity and alkalinity.

Calcium is most likely to be deficient in the diet of young birds and provision of calcium in the form of soluble grit is essential. Certain disorders of the kidneys and gut, however, may lead to a deficiency owing to inadequate absorption. Osteomalacia is the result of deficiencies or abnormal ratios of calcium to phosphorus in the diets of chicks and adults respectively. Brittle and easily fractured bones, result from these two diseases. The clinical and radiographic changes seen in the bones of young parrots and other young birds are sometimes similar to those reproduced in dogs on a diet containing normal amounts of calcium and very high phosphorus, with normal or high vitamin D3 intake. In breeding birds, shell_less or thin_shelled eggs are often laid and the embryos are stunted or chicks weakly on hatching. Although phosphorus comprises barely 1 per cent of the shell of eggs, it is nevertheless essential to its construction. It is also present in chemical combination in egg yolk. When birds are breeding, the extra phosphorus excreted is much greater than that used in the egg itself. Species which will eat manufactured crumbs or meals can be given a bone-meal additive to maintain a favorable calcium, phosphorus and magnesium intake.

Phosphorus is important in the metabolism of fats and carbohydrates. It is combined mainly with calcium in bone and egg-shell, as well as being an important constituent of all living cells, especially muscle. In severe kidney disease, the calcium stores of the body are squandered while phosphorus is retained. The role of vitamin D3 in calcium and phosphorus metabolism has been discussed above and is also referred to under skeletal disorders. Phosphorus is widely distributed, occurring in plants, milk and fish.

Magnesium, although found in the body in much smaller quantities than calcium and phosphorus, is also an essential constituent of bone. Most of the mineral is present as a carbonate. Egg-shells also contain an appreciable quantity of the mineral and it is necessary for carbohydrate metabolism. Most diets contain magnesium and it should not be necessary to provide supplements.

This is seldom deficient in the diet because it is present in most avian foodstuffs, often in association with calcium and phosphorus. An excessive intake may lead to diarrhea, possibly nervousness in poultry, and even deformed bones as a result of interference with the balance of calcium and phosphorus; but the latter minerals in adequate amounts and proportions will permit tolerance of a moderate excess. The mineral is essential for carbohydrate metabolism and in certain enzyme activities. Neither deficiency nor excess of either are likely to occur in cage birds owing to the high proportion of natural food usually fed and the unlikelihood of salted food being available or accepted by them. Extremes of both interfere with normal growth; excess produces severe thirst, weakness and possibly convulsions prior to death. Deficiencies are more likely to arise from an undue demand by the body for these elements when vomiting or serious exudation occur.

Potassium is found primarily in the cells of the body, including bone. It plays a role in metabolism which is not clearly understood and is necessary for the oxygen-carbon dioxide exchange in red blood cells and for normal activity of the heart, having a relaxing effect by reducing contractility, the opposite effect to that of calcium. Potassium allows certain chemical exchanges through the cell membranes to occur more easily. The mineral is widely distributed in food of both plant and animal origin so that deficiencies are unlikely to occur. This is so readily available in natural foodstuffs that a deficiency is improbable. The mineral is essential for the metabolic processes of the body and for the formation of all body tissues.

Sodium is usually combined with chlorine to produce common salt or sodium chloride and is found mainly in the fluids of the body (blood and lymph) in contrast to potassium, which occurs inside cells. The sodium content helps to keep the body from becoming too acid, being involved in the acid-base equilibrium and regulation of the pH of the blood which prevents marked changes in acidity or alkalinity. Together with potassium and calcium in proper balance, it is essential for heart activity.

Excess chloride is discarded in the urine, while some is retained for use in digestion as hydrochloric acid. As sodium occurs fairly widely in combination with chlorine or as the carbonate or phosphate of compounds, especially in foods of animal origin, it is seldom necessary to supplement the diet of cage or aviary birds. Should this seem necessary, it must be done with great care as an excess of salt is toxic to many birds.

Iron & Copper:
Iron deficiency can result from hemorrhage, from wounds for example, but more commonly from attacks by mites or ticks. Ulcers and other lesions that cause repeated small blood loss can also have a similar effect. Normal requirements are greatly raised when birds are laying and deficiencies may occur. Iron is closely linked with copper in the production and maintenance of blood and the constituents of eggs. Excessive iron supplied in the diet is not absorbed and is therefore harmless, but excessive copper is highly toxic, building up in and damaging the liver and other active organs. When copper is low in the diet, iron is absorbed and stored in the liver and is not used adequately in the manufacture of the blood pigment haemoglobin. Anemia then results.

Sulphur is a constituent of certain amino-acids, methionine and cystine, used in the formation of muscle protein, egg yolk, egg albumen and keratin in skin, horn and feathers.

This is obtained in adequate amounts whenever the bird eats enough good quality protein, containing a high proportion of the amino-acids cysteine and methionine. Plant foods supply sulphur unconnected with organic substances in the simple inorganic forms such as ferrous sulphate. Egg contains a very high proportion of sulphur, and the characteristic smell of bad eggs is due to the production of hydrogen sulphide. A minute amount of sulphur is supplied by the vitamins aneurin and biotin. Even during laying, deficiency is unlikely to occur; but if it does, it will show itself largely as the thio-amino-acid deficiency (see protein deficiencies) which affects feathers, skin, heart, muscular and glandular tissues, as well as egg production.

Iodine is used almost exclusively by the thyroid gland. Without it the hormone thyroxine, secreted by the gland, cannot be made. Iodine is liable to be deficient inland in areas where it is lacking in the soil and where birds eat nothing but local-grown food. Breeding increases the body's requirements for this element, so the young of parents on the borderline of insufficiency are most likely to show clinical signs of iodine deficiency such as thyroid disease or goitre. Fish-eating birds fed on sea fish derive adequate amounts of iodine from their diet and this type of goitre is hence unknown in seabirds. Even the oyster shell used as soluble grit contains an appreciable amount of iodine and so occurrences of goitre are comparatively rare except in budgerigars.

Enlargement of the thyroid gland in adult budgerigars is mostly the result of iodine deficiency; the affected gland contains inactive secretion, resulting in a lowered metabolism, sluggishness, ragged plumage with loss of pigmentation and a general slowing of bodily activities. In budgerigars, the most characteristic sign is labored breathing associated with squeaking noises, this being due to pressure of the enlarged thyroids on the syrinx and lower trachea. In chicks and nestlings, the deficiency results in stunted growth and retarded mental and physical activities. Provision of an iodized supplement rapidly removes the clinical signs of disease except in far advanced cases. Many compounded cage-bird foods are nowadays impregnated with iodine. Certain foods can lessen the effect of the iodine available in the food; soya bean is an example.

Deficiency of manganese may play a part in the formation of enlarged hocks and slipped tendons sometimes found in growing cage birds, but this is not certain. Investigations into the role of the mineral in French molt of budgerigars have brought forth no definite evidence of this disease coming from manganese deficiency. The shortening and deformity of bones and spinal column in growing poultry when the diet is manganese-deficient, have not yet been reported in cage-birds but this is probably due to lack of research: this also applies to poor bone formation in the skeleton of the embryo and mortalities in the last third of the incubation period. Chemical analysis of bone and tissues would establish whether this or other deficiencies are responsible.

Manganese is only known to be essential for avian development by the bone and joint defects such as perosis which result from its deficiency, though it may play a part in egg production.

Other Trace Elements:
The roles of molybdenum, selenium and zinc are incompletely known in cage birds. They probably assist in the development and maintenance of certain tissues. Cobalt is important only inasmuch as it is part of the vitamin B 12 molecule. If this vitamin is adequately synthesized by bacteria, no extra cobalt is required.

Other elements and trace elements are required in much smaller amounts; yet their lack can lead to spectacular effects.
IRON is well known as a constituent of the hemoglobin of the blood, but even smaller amounts of COPPER are necessary as well for the formation of this pigment. Iron and copper are also necessary for the function of various enzymes and, as with other essential chemicals, they are required in increased quantities during the period of egg production. Stores of iron are present in the liver.

FLUORINE may play a part in bone metabolism of birds, although this is doubtful. The main interest of this element is that toxic levels can occur in birds and poisoning result if large quantifies of fluorine-containing minerals are fed.

SELENIUM is another element of doubtful necessity in cage birds although it may help in the retention of vitamin E. In the domestic fowl it prevents encephalomalacia ("softening" of the brain) and muscular dystrophy.

ZINC seems to be necessary in minute quantities for all warm-blooded creatures being essential for growth. In poultry, high intakes of dietary calcium increase the requirements of zinc.

MOLYBDENUM is also necessary for normal growth. The roles of molybdenum, selenium and zinc are incompletely known in cage birds. They probably assist in the development and maintenance of certain tissues.

COBALT, the metallic atom in vitamin B12, does not appear to be necessary alone for birds, providing that vitamin B12 is supplied in sufficient quantities in the diet or is synthesized by gut bacteria. Cobalt is important only in as much as it is part of the Vitamin B12 molecule. If this vitamin is adequately synthesized by bacteria, no extra cobalt is required.

About 70 per cent of the tissues of most higher animals consists of water. Birds cannot, as flying creatures, carry excess water. The amount consumed differs considerably between individuals as well as between species. In cases of poisoning by common salt, for example, there is a great increase in thirst. Fruit-eating birds such as mynahs and lorikeets, seldom need to drink. Their problem is to eliminate the excess water. This results in extremely sloppy, watery droppings in which both the urine and faeces fractions are highly diluted. The appearance of the excreta should not be mistaken for diarrhea or kidney disease.

Water is needed for every chemical process of the body and since the amount of "spare" water lying in the various parts of the alimentary tract at any one time is small, it must be available at all times. Withdrawal of water can rapidly produce distress in many species, especially in a high environmental temperature. It leads to panting, gaping, collapse, convulsions, and death. Much water is lost via the lining membranes of the respiratory system. Respiratory water loss cannot be easily controlled and in fact increases when the bird becomes distressed. A small amount of water is lost in urine and faeces but it is regulated largely by the re-absorption of water in the large intestine.

It will be appreciated that because of the great variation of water intake in the diet, and the relative humidity of the environment, the use of medicated drinking water for treatment is a relatively inaccurate method of dosing.

Everyone knows how bad water can kill people so it is so possible that a problem with your water can harm your birds, especially if you allow food or droppings to get into the water and contaminate it. The intake of water, its utilization and excretion involve a very delicately balanced mechanism. Birds do not carry much useless water around with them in the form of urine. Nevertheless, their tissues contain almost 70 per cent water. Certain centres in the brain govern thirst and water intake; these are operated by changes in the chemical content of the blood, and this in turn is dependent on how much water is taken and excreted. A bird has the normal stimuli to drink, but during some illnesses abnormal ones operate.

These illnesses are salt or arsenic poisoning, when there is a high temperature associated with certain infections; heatstroke; loss of fluid by evaporation from panting in respiratory disease; loss of fluid in regurgitation, vomiting or diarrhea; and when there is irritation to the kidneys. Excessive thirst is not always accompanied by loss of abnormal fluid. Even when it is, water intake cannot always keep up with water wastage. Soluble minerals and food substances are also lost when excessive vomiting, diarrhea, or increased urine output occurs and these losses are not made up by drinking. Mineral deficiencies or imbalance will therefore result. Water input, output, and re-absorption by the kidneys and gut are controlled by hormones from the pituitary and adrenal glands, which can influence the blood flow to the kidneys. Very many different diseases may interfere with some stage of these processes, which are designed to maintain a uniform balance of water in the bird and are mentioned elsewhere.

Roughage or Fibre:
Roughage is coarse food high in fiber but low in nutrients; its bulk stimulates peristalsis. Mammals and birds have evolved to occupy a special place in nature. Each has become adapted to its changing environment and the availability of its food and, as Darwin discovered, only the fittest and most adaptable survive to thrive in this niche. Apart from most plants and some primitive and parasitic forms of life, animals depend on food manufactured from the bodies or remains of other living creatures. Their food is thus a mixture of the digestible, absorbable, and indigestible. In times of food shortage, the readily digestible and absorbable ingredients are scarce while the intrinsically valueless ones are available. Individuals with digestive processes most efficient at dealing with poorer quality food are therefore more likely to survive and breed.

Birds and mammals have an efficient digestion, each species with its own modifications enabling it to deal with a wide range of plant or animal food material. Part of that efficiency depends on the maintenance of tone or muscle power in the complicated tube comprising the alimentary canal or gut. The muscular tone of the gut depends on work, like its counterpart in the skeletal musculature. Dealing with roughage ensures that the muscles of the gut and also the secretory activity of its glands are exercised and maintained. A sick bird can be kept for a short period on readily absorbable liquid foods. If on recovery, however, it is suddenly provided with normal food only, a digestive upset is likely.

Dietary requirements vary considerably in birds from the predominantly nectar, fruit and flower-eating species, through the insectivorous, flesh and carrion eaters, to the grain, grass, and bark feeders. Fruit and flowers, although very high in water content, are also quite rich in fiber. No flying bird can afford to carry much surplus weight and the quantity of food carried in the gut of most species at any one time tends to be smaller than with purely terrestrial animals. Nevertheless, some roughage is needed by almost all birds. It is also needed to give a favorable environment for multiplication of the micro-organisms which aid digestion and produce such vital substances as vitamin B12. If the percentage of roughage is greatly increased, there is a tendency for impactions of the crop, gizzard, or sometimes the intestine to occur, these being most frequently seen in badly nourished and debilitated birds.

A diet high in fibre is often low in nutriments, and the functions of the gut are then impaired. A deficient bird is a weakened one and therefore the muscular power of the gut is also weakened. A laxative should be given followed by a more concentrated but easily digested diet: soaked or sprouted seed, egg, milk, cheese, liver, yeast or gentles, according to the species concerned. Treatment of impaction of the crop is dealt with elsewhere. Insufficient fibre tends to produce a small amount of pasty, tenacious feces which may matt the vent feathers or cause constipation. Under these circumstances the urinary excretion forms a relatively higher proportion of the droppings. When birds are fed concentrated diets lacking in fibre, there is a tendency for kidney disease and gout to occur.

Predominantly grain-eating birds, especially pigeons, are seldom affected with either excess or lack of fibre, although an unaccustomed bird allowed out into an aviary planted with grass and weeds may gorge itself on this roughage; mineral deficiencies can make birds more prone to this habit. Crop and gizzard impactions are particularly common in large omnivores such as ostriches, emus, rheas and bustards. Members of the parrot and crow families, often given human food such as scraps and cake, are most likely to suffer from lack of roughage and it can lead to wasting or atrophy of the gizzard and gut muscles. Species such as fruit and nectar- eating birds with poorly developed gizzards do not appear to need fibre.

Insoluble grit is essential in the diet for seed-eating birds which have a well developed muscular gizzard. The grit aids in the grinding of the seeds and other hard particles of food, and should therefore be hard with sharp edges, for example, quartz. If the grit is too fine it will fail in its function and may cause impaction of the gizzard. It is equally important that the particles are not too large for the size of the bird. Special grit for cage birds can be purchased, but where birds are kept in aviaries with a soil base this is not so important as the birds may find suitably sized particles for themselves. Insoluble grit should NOT be considered as a source of minerals. These may be provided in the form of such substances as broken-up oyster shells and cuttlefish bone.



E-Mail: berniehansen@sympatico.ca



- TOP -

Hamilton & District Budgerigar Society Inc.