Nutritional Disorders in Poultry and the Role of Nutrition in Disease Prevention

Animal Nutrition Division

ICAR-National Dairy Research Institute

Karnal-132001 (Haryana) India

Nutrition is the science of nourishing the body.  Nutrients are substances that nourish living creatures. These are water, carbohydrates, proteins, fats, minerals and vitamins, present in different feedstuffs in variable quantity. All the nutrients are essential for growth, reproduction, egg production and good health of the birds and are supplied through diet. However, when these nutrients are deficient in diet they not only limit the growth and production, but also cause certain deficiency diseases or conditions depending upon the degree of deficiency as well as duration of deficiency. The characteristic features of these diseases are that most or many of the birds in a flock will show similar type of symptoms which may be either mild or well developed, because all the birds get the same feed stuff. Nutritional diseases generally produce retardation of growth or other symptoms which are characteristics in some cases. Mortality is not sudden and serious in most of the deficiencies and growing birds are mostly affected due to their specific requirements for body growth. Another factor which should attract our attention regarding nutritional deficiencies is fall in hatchability and some embryonic pathological changes due to deficiency in the layer stock.

Nutrient deficiency diseases/conditions/disorders

(A) Water: Water is an essential constituent of animal body and its content is about 70% at hatch, 60 to 68% at 6 weeks of age and as low as 52-57% when adult. Water plays a significant role in animal body. Deficiency of water leads to dehydration, accumulation of uric acid (gout), depressed feed intake and growth, haemoconcentration, lower blood volume, increased heart and respiration rate, and death. The requirement of water for poultry birds is calculated mainly on the basis of feed intake. The ideal ratio of water to feed intake is 1.50- 2.50: 1. The water intake for growing birds is about 2-2.5 times of feed intake during summer and 1.5 to 2 times of feed intake during winter. The layers consume generally 1.8-2.2 times in winter and 2.6-3.5 times in summer. When room temperature exceeds 35°C, the water intake may be even 4.5 times to that of feed intake.

(B) Protein and amino acids: Proteins consist of many amino acids of which some are essential for the birds. Deficiency of some of the amino acids may lead to symptoms like feather pecking, cannibalism, ruffled feathers (due to arginine deficiency), perosis or slipping of gastrocnemius tendon (due to deficiency of sulphur containing amino acids like methionine and choline. etc.) Layer chicks require 21 per cent and broilers 22.5 per cent crude protein. More than one type of protein sources in the feed mixture may help in the prevention of such conditions. Most prominent symptoms are seen as a result of deficiency of lysine, methionine and choline amino acids in particular, which in addition to producing symptoms mentioned above cause retardation of growth and egg production. Methionine also acts as a precursor for vitamin B12 and choline synthesis. Choline also helps in metabolism of fat and its deficiency may help fatty liver syndrome. The protein sources are classified into animal and vegetable protein supplements depending upon origin. The animal protein sources include fishmeal, meat meal, meat-cum-bone meal, blood meal, etc. The oil cakes and meals like soybean meal; groundnut cake, rapeseed meal, sunflower seed meal, maize gluten meal, sesame/til meal, etc. are some of the common vegetable sources of protein.

(C) Fats and Essential fatty acids: Deficiency of fats or oils in the diet decreases feed intake and may lead to deficiency of fat soluble vitamins and essential fatty acids. Essential fatty acids are not synthesized in the body and thus are dietary essential i. e. must be supplied through diet. The essential fatty acids are linoleic and arachidonic acids in poultry. Deficiency symptoms include retarded growth, loss of feather, scaly skin, diarrhorea in young chicken and reduced egg size, reduced egg production and marked decrease in hatchability in layers/breeders. Generally the requirement of linoleic acid is 1% of diet, and to meet its requirement diet should contain 3% oil (feed/supplementary). The oils are preferred over fats because the former contains more of unsaturated fatty acids. The different vegetable oils that can be used in poultry feeds are soybean oil, maize oil, til oil, palm oil, coconut oil. Animal fats like lard or tallow can be used alone or with oils for their improved utilization.

(D) Vitamins: Birds require almost all the vitamins through feed products. The requirement of only vitamin C is debatable. Vitamin deficiency, particularly which of B-complex group, generally occurs in a combined manner. Sometimes, in spite of the presence of proper amount of vitamins in the feed they may get destroyed due to improper storage and may result in deficiency diseases. Such vitamins are vitamin A, D and E which easily get destroyed by the oxidation process. Pantothenic acid and thiamine also undergo early destruction.

(i) Vitamin A: Deficiency of this vitamin is encountered quite commonly. Nowadays, many concentrated products of vitamin A are available in India. It is also called as infection resisting vitamin, because proper development of the epithelium, bursa of Fabricius and immunity is dependent on vitamin A which plays a vital role in the disease prevention. It is essential to add 1200 IU of vitamin A per 400 g of feed for chicks and 2000 IU of vitamin A per 400 g of feed for layers and breeders.

Symptoms: The symptoms of vitamin A deficiency develop several weeks after feeding deficient diet. Symptoms are not pathognomonic but may include weakness, imbalance, retardation in body growth, ruffled feathers, loss of yellow colour of the shanks and abnormally large combs and testes. Highly deficient chicks become prone to conjunctivitis, chronic respiratory disease (CRD), coccidiosis and other infections. In new born chicks, symptoms develop after 4 to 7 weeks of age. If breeder flock is deficient in vitamin A then embryonic deaths occur more frequently and table eggs may show blood spots.

Lesions: Mucosal surface of the oesophagus shows most characteristic changes. Swollen glands may take the form of vesicles or pustules, 1.5 to 2 mm in size. Ulcers may form in the mouth which gets covered with cheesy exudates, resembling lesions of fowl pox. Cheesy exudates may also be encountered on the palate and in the nostrils. In well-developed cases, dry flakes are found in the respiratory tract which may give suspicion of ILT. In young chicks bursa may also show cheesy exudates. It may also lead to deposits of urates in kidneys and other organs.

Ducks exhibit symptoms of imbalance, lameness and even paralysis. This happens because of the improper ossification of vertebral osteoid leading to pressure on the nerves. Uric acid gets deposited in the kidneys, liver and other visceral organs.

Mortality rate is dependent on the extent of vitamin A deficiency and secondary infections. It has been recorded up to the extent of 8 per cent.

Diagnosis: Tissue alternations in the oesophagus and respiratory tract are highly diagnostic for moderate deficiency of this vitamin. Twisting of the head to one side and improper development of main blood vessels is commonly seen in embryos, deficient in vitamin A.

Requirement: For treatment 12,500 IU of vitamin A and 1/5th of this quantity of vitamin D should be mixed in every kg of the feed. High temperature, dampness, excess of manganese and calcium in the feed have destructive effect on the vitamin. Fish liver oils, green pasture, dried leaf meal, yellow maize, maize gluten meal and vitamin A supplements. One milligram of b- carotene is equivalent to 1667 IU of vitamin A. Vitamin A is commercially available as premix alone (vitamin A acetate)or with other vitamins (B2, D3 and K).The requirements are: Starting chicks 4000 IU/kg, broiler 6000 IU/kg, laying hens 8000 IU/kg and breeding hens 12000IU/kg diet. Storage of compounded feeds for longer period increases the possibility of vitamin A deficiency.

(ii) Vitamin D: Vitamin D is also called “antirachitic factor”. Cholecalciferol (D3) is the most potent than D2. The birds exposed to sunlight generally do not exhibit signs of vitamin D deficiency. However, under intensive production system deficiency may occur. The symptoms include:

Chicks: Retarded growth, rickets (reduced bone mineral deposition): characterized by severe weakness of legs, soft and brittle bones, soft, rubbery and pliable claws, bowed/bending of legs, spread out toes and swollen hocks ; poor feathering ; blacking of feathers and rubbery beak. Heads of ribs and epiphyses get enlarged.

Layers: Drop in egg production, soft and thin shell egg formation, reduced hatchability; eggs without shell and fragile bones, sternal recumbancy due to osteomalacia (bone mineral loss) are usual features.

Turkeys and ducks: Symptoms are similar to those of chicks Beak can often be fedded back on itself in ducks.

Fish liver oil, exposure to sunlight/ ultraviolet light and vitamin D3 supplements. Seeds and their byproducts are practically devoid of this vitamin. The requirements are 200 –600IU per kg diet of broiler and starting chicks, and 400- 1200 IU per kg diet of laying hens.

(iii) Vitamin E: Since vitamin E has got antioxidant properties, it helps in the preservation of other vitamins like vitamin A, D and fatty acids, etc. This vitamin has got complimentary relations with selenium and cysteine. It has got preventive effect against the degenerative changes of muscles and exudative diathesis. Deficiency of vitamin E and the other two factors may lead to the following conditions.

(a) Avian Encephalomalacia: This disease is most commonly seen in 2 to 6 weeks old birds. The author has also seen this disease in broilers, pheasants and peafowls.

Symptoms: Due to the characteristic symptoms, the disease in chickens is also called as ‘crazy chick disease’, because the diseased chick appears to push its head beneath its breast. Finally chicks show paralysis. Similarly symptoms may also develop due to vitamin A deficiency, but under that condition lesions are not seen in cerebellum. Diseased birds die within a few days. Mature birds do not show any symptoms except drop in egg production. Male birds may show degenerative changes in the germinal epithelium of the testes.

In the chicks, haemorrhages are seen in the cerebellum and medulla oblongata. It may also show areas of necrosis and oedema, with haemorrhages at the periphery. Lesions sometimes may affect 3/4th of the cerebellum or sometimes they may even be microscopic.

Prevention and treatment: For prevention, vitamin E should be given at the rate of 55 IU/kg of feed, whereas for the treatment 300 IU of vitamin E/kg of feed is essential. Cotton seed cake, soybean oil, etc. are good source of vitamin E.

(b) Exudative Diathesis: Under this condition, oedema is encountered in the subcutaneous tissue, which later turns green due to lysis of blood. Oedema is commonly seen in the ventral aspect of the body and pericardium. Birds develop moderate anaemia and haemorrhages in the breast, thigh, intestine and gizzard. These lesions may also be seen in association with muscular degeneration. The disease occurs in almost the same age group of birds as described under avian encephalomalacia or it may also be seen in slightly older birds.

For the treatment, adequate amount of vitamin E should also be supplemented with 1.2 mg selenium/4 litres of water. Synthetic antioxidants like methylene blue, added to the diet, can also prevent the disease.

(c) Muscular Dystrophy: This disease develops in chickens due to deficiency of vitamin E and sulphur containing amino acids like methionine. In ducks, only vitamin E deficiency will lead to muscular dystrophy. The disease is commonly seen at 4 weeks of age in ducks, chickens and turkeys. White, necrotic areas of muscles are seen in the breast muscles but in the ducks and sometimes in other species too, necrotic areas along with oedema may also be seen. In turkeys lesions in gizzard develop due to combined effect of vitamin E and selenium deficiency.

(iv) Vitamin K: Normally Vitamin K is not deficient in mash. It is abundantly present in the green vegetables and grass. Although microbes present in the intestine of birds do synthesize some amount of vitamin K but it is not sufficient to complete the dietary requirement. Probably some of the fungal toxins and sulpha drugs may have inhibitory effect on vitamin K synthesis. Deficiency of vitamin K is considered to be one of the etiological factors of haemorrhagic syndrome in poultry. Addition of vitamin K at the rate of 25 mg/kg of feed is sufficient to prevent the disease but its quantity should be increased if the birds are undergoing treatment with sulpha drugs. Chicks: Hoemorrhages on the breast, legs, wings and abdominal cavities, a bluish-netted appearance to the skin and death due to bleeding are seen in boarder line deficiency. Severely deficient birds may bleed to death. Adult birds: They do not show haemorrhagic symptoms. But inadequate vitamin K in breeder diet may cause late incubation period and embryonic mortality.

Green forages or leafy materials (spinach, cauliflower, cabbage), soybeans, wheat bran, liver meal, fishmeal, egg yolk are the good sources of vitamin K. The commercial source is Vitamin K₃ IP or menadione. The requirement is 0.5mg per kg of diet for all categories of birds.

(v) Thiamin (vitamin B1): This vitamin is required for energy utilization and prevention of star-gazing or polyneuritis condition. Thiamin deficiency is associated with accumulation of pyruvate and lactate in blood, reduced synthesis of fatty acid and energy metabolism. In chicken and turkey, deficiency occurs after 9 to 12 days when the day-old chicks or poults are kept on deficient diet.

Chicks: Polyneuritis or stargazing (pulling of head towards back) is the syndrome. The symptoms are loss of appetite, emaciation, general weakness, convulsion, digestive impairment, and paralysis of wings. The head is pulled towards its back because of paralysis of extensor muscle in neck. Similarly, paralysis of extensor muscles of leg causes the bird to sit on hocks. This condition is termed as stargazing or polyneuritis. Yeast, wheat germ, rice polish, whole grain & their byproducts, lucerne meal, liver meal and synthetic vitamin B1 (aneurin hydrochloride or thiamin hydrochloride).

Requirements: Broiler 2mg/kg diet, starting chicks and laying hens 6 mg/kg diet. Amprolium also decreases intestinal absorption of vitamin B1.

(vi) Riboflavin (vitamin B2): Riboflavin helps in the synthesis of many oxidizing enzymes. Symptoms: This vitamin is essential for normal metabolism in body. Its deficiency affects nerves, embryos, body growth etc. Important symptoms include inward curling of the toes and sitting on the hocks. The disease is also called as “curled toe paralysis”. At about 10 days of age diarrhoea develops. The birds also show drooping of wings and head and dermatitis of eyelids, feet and mouth. There is slight decline in egg production in layers.

Laying and brooding capacity of adult birds is considerably reduced. Embryos from such eggs become atrophic and oedematous and their feathers give typical, clubbed appearance, especially in feathers of neck and back because the sheaths of feathers do not mature. There is embryonic mortality at 2nd or 4th weeks of incubation.

The sciatic nerve of the diseased chick or affected embryo becomes 3 to 4 times thick, oedemtous and soft due to myelin degeneration and Schwann cell proliferation.

Prevention and Cure: For prevention, riboflavin should be given at the rate of 2 gm/ton of feed. For treatment, the amount of riboflavin in the feed should be increased by 5-10 times the normal. Up to 6 weeks of age, chicks must get twice the normal amount of riboflavin in the diet.

Turkey and ducks: In poults deficiency causes reduced growth rate, perosis, poor feather development, severe dermatitis of feet and shanks marked by oedematous swelling, grow poorly. In ducks in addition to these symptoms, increased mortality is also seen.

Liver meal, yeast, rice bran, molasses, fishmeal,  lucerne, milk products and synthetic B2. Yeast is the richest natural source (125ug/ g). Leaves and leafy forages are also good sources. The requirement is 5 mg per kg diet.

(vii) Niacin: This vitamin is synthesized form amino acid tryptophan in the diet with the help of vitamin B6. This vitamin is an essential component of nicotinamide-adeninedinucleotide (NAD), diphospho-pyridinenucleotide (DPN) and nicotinamideadenine-dinucleotide-phosphate (NADP) which are essential for the metabolism of carbohydreates, lipids and proteins.

Symptoms: Symptoms of niacin deficiency are shown by growing chicks, turkeys and ducks. The hock joints becomes enlarged and the legs bend outwards, as seen in cased of perosis. But in this disease the gastrocnemius tendon retains its original position. In addition, symptoms like diarrhoea, stomatitis, oesophagitis and improper development of feathers have also been recorded. As in vitamin B1 deficiency, the egg production and hatchability also declines. Prevention and Cure: For prevention, wheat bran, yeast, rice-polish, fish meal, etc. should be given in the feed which are good sources of niacin. Rice polish, molasses, wheat bran, groundnut cake, lucerne meal and synthetic vitamin (Niacinamide IP, Niacin IP) are the sources of niacin. The requirements are: Broiler 40mg/kg, starting chicks 30mg/kg, and laying hens- 20mg/kg diet. (viii) Vitamin B6 (pyridoxine): Metabolities of vitamin B6 such as pyridoxal or pyridoxamine phosphate are more active than pyridoxine. In nature, pryridoxine and its metabolites occur together. This vitamin helps in the metabolism of amino acids.

Symptoms: Deficiency of vitamin B6 results in stunted growth, staggering, incoordination in the movement and encephalomalacia. Some of the birds may show jerking movements or convulsions of legs and wings, resulting in rolling onto back with legs upward. The birds may run aimlessly with flapping of wings and death. Mature birds show loss of appetite, drop in egg production and hatchability.

Vitamin B6 is distributed among the plants & animal foods of the diet. Yeast, cereal grains and their byproducts, liver meal, synthetic vitamin (vitamin B6) are the best sources of this vitamin. Generally the food supply is sufficient to meet physiological requirement of pyridoxine. The requirement is 3 mg per kg diet for all categories of chicken. Linseed has inhibitory effect on pyridoxine.

(ix) Pantothenic acid: This vitamin is also called as bird antidermatitis vitamin. The deficiency of this vitamin is not common as compared to others. This vitamin is essential for the synthesis of coenzyme A which is required for the metabolism of carbohydrates, proteins and lipids. Symptoms: Most prominent symptoms consist of formation scabs at the commisures of the mouth, sometimes eyelids and toes. Deficient birds may also show stunted growth and ruffled feathers. Another important change consists of noduar hyper-plasia or cracks in the skin of foot pad, at the joints of the claws. Later the skin and these sites may develop cracks at some places. During postmortem, spleen shows sypoplasia. Liver is small and yellowish. Yellow, pus-like material may be found in the mouth and proventriculus. There is increase embryo mortality by about second week of incubation. The embryos show subcutaneous oedema and haemorrhages. The natural sources of this vitamin are yeast, liver meal, groundnut meal, green gram, lucerne meal, milk products, fermentation residues, cereal seeds and byproducts and cane molasses. Synthetic source is calcium or sodium salt of the d- isomer (active form). The calcium salt (calcium pantothenate)is the most common commercial form as it is relatively less hygroscopic. The requirements are: Starting chicks 10mg/kg, laying hens 15mg/kg and broiler 12 mg/kg. The requirements of turkey are almost double that of chicks and they are at risk even at normal diet. (x) Biotin: The condition “egg white injury” is due to biotin deficiency. A toxic mucoprotein is present in egg white called avidin. Avidin combines with biotin to form an insoluble complex that is not absorbed from intestinal tract and renders biotin unavailable. Deficiency of biotin is unlikely under normal dietary conditions. Artificially created deficiency symptoms are:

It is known that egg contains a protein which has got inhibitory effect on the biotin, if raw egg is consumed by human beings. The raw egg component combines with biotin in the intestine and interferes in the absorption of biotin.

Symptoms: Deficiency of biotin is rare because of its presence in the diet in sufficient amount, naturally. Like pantothenic acid deficiency, it also produces dermatitis, perosis etc. Deficiency in layers caused embryonic death either in the first week or during last 2-3 days of incubation. Dead embryos show parrot beak, distorted limbs and big web between 3rd and 4th phalanges.

The natural sources are Yeast, groundnut cake, green leaves, molasses, sunflower meal, liver meal. Wheat and corn products are poor sources. It is available as vitamin H or biotin (2%).

Requirements: Broiler and starting chicks 0.10 mg/kg and laying hen 0.15 mg/kg diet.

(xi) Vitamin B12: It is also called animal protein factor. It is required for growth (thus called chick growth factor) and to prevent anaemia (antipernicious anemia factor). The deficiency symptoms are:

Chicks: Retarded growth, poor feathering, increased mortality rate.

Layers: Reduced egg production.If laying birds are deficient, hatchability may drop to zero in about 6 weeks, mortality in embryo(peak at 16-18 day) with malposition, myoatrophy and chondrodystrophy, embryos are oedematous, haemorrhagic with an irregular shaped heart.

The sources are fishmeal, meat meal, liver meal, cow dung and synthetic vit. B12. The origin of the vitamin in nature is probably the result of microbial synthesis. Plants feeds are devoid of this vitamin.

Requirements: 0.015mg per kg diet.

(xii) Vitamin C: It is chemically known as L- ascorbic acid. Deficiency of vitamin C usually does not occur in chicken. However, its supplementation (@ 100 mg/kg) is beneficial to increase the livability of birds under heat stress. The sources are fresh fruits specially citrus & leafy vegetables.

(E) Essential Minerals

(i) Calcium (Ca): It is the major element, present in largest quantity in the body and has both structural and biochemical functions. The deficiency symptoms are:

Chicks: The deficiency symptoms are similar to that of vitamin D. Stunted or no growth, unwilling to walk, lameness, rickets (enlarged hocks, beaded ribs, deformed sternum and spine, rubbery beak and leg bones).

Layers: Frequent squatting posture, reduced egg production, thin shelled eggs, eggs without shell, decreased hatchability due to poor egg shell quality and more egg weight loss, fragile bone, leg weakness of caged layers. Deficiency of calcium leads to deformation of egg shell, thin shell egg, egg without shell. Cage layer fatigue condition is a disease of layers (hens and turkeys) reared in cages characterized by soft, weak and fragile bone. The leg bones become so weak that legs do not support the weight of the birds. The condition is associated with feeding of low calcium and high phosphorus diet. The laying birds reared on floor do not suffer from this condition.

The different sources of calcium supplements are limestone (34% calcium), oyster shell (34% calcium), marble grits or powder (34% calcium), bone meal (steamed or sterilized 24% calcium), bone ash (36% calcium), di-calcium phosphate (22-28% calcium) and rock phosphate (33% calcium).The requirements of calcium in diets are broiler starter 1.0%; broiler finisher 0.9%; egg type starter and grower 1%; layer 2.75-3.5% depending upon egg production and size of eggs. A free access to shell grit/ marble chips should be made available during peak production of eggs besides the dietary supply. The requirement of calcium is met partly by coarsely ground calcium carbonate (2-3 kg/100 kg feed) and remaining through oyster shell grit/ marble grit.

(ii) Phosphorus (P): It is component of bone and many organic molecules. The deficiency symptoms are:

Chicks: Loss of appetite, weakness, growth failure, rickets as in calcium or Vitamin D deficiency.

Layers: Loss of appetite, reduced egg production and shell strength, cannibalism or feather pricking.

The cereals and their byproducts are good sources of P but availability of P is less from those ingredients (average 30% is available). Bone meal (steamed 12% phosphorus), bone ash (17% P), di-calcium phosphate (19% P), rock phosphate (18% P), sodium acid phosphate (22% P), etc. are the supplementary sources. The requirement of available P ranges from 0.45 to 0.30% in broilers and growing egg type chicks depending upon age and 0.30 to 0.35% in layer diets. The requirement of available P for turkey birds ranges from 0.60% at early age to 0.25% at market age, and 0.35% during laying. The requirement of total phosphorus is 0.6 to 0.7%.

(iii) Manganese (Mn): It is an important mineral for reproduction and is involved in several enzyme systems. The deficiency symptoms are:

Chicks: Perosis (swollen and flattened hock joints, slipped tendons), shortening and twisting or bending leg bones. Perosis may also result due to choline, folic acid, biotin, niacin and zinc deficiency.

Layers: Reduced egg production, egg shell strength and hatchability, thin shelled or shell–less eggs, nutritional chondrodystrophy in embryonic chicks (shortened and oedema thickness legs), shortened wings, parrot beak, retarded growth and oedema. Embryos of manganese deficient birds show heavy mortality during the last phase i.e. after 18 days and peak in 20-21 days of incubation.

Grains are usually deficient in manganese. Borderline deficiency in feeds exists. Lucerne meal, grain byproducts and manganese salt (sulphate, 25% Mn, and oxide, 60% Mn) are some sources of manganese. The requirement is 30-50 mg per kg diets.

(iv) Zinc (Zn): Zinc is required for growth, feathering, egg production and hatchability. It is associated with many enzymes as an essential component or activator. Zn is not stored sufficiently in the body for longer period. The deficiency symptoms are:

Chicks: Loss of appetite, retarded growth, poor feathering, shortening and thinning of bones, enlarged and rigid joints, enlargement of hock joint, scaling of skin and the limbs become thickened due to scales hence the disease is also called scaly limb disease.

Layers: Decreased egg production and hatchability. Embryonic mortality peaks around mid incubation with defective embryo (missing or underdeveloped toes and eyes, deformed skeletal formation), caused by zinc dependent metabolic processes involved in the development of skeletal mesoderm. Hatched chicks are weak and cannot stand, eat or drink.

Feedstuffs are mostly deficient in zinc, thus its supplementation is required. Zinc oxide (73% Zn), Zinc carbonate or Zinc sulphate (36% Zn) are the supplementary sources of zinc.

Requirements: 40-60 mg per kg diet.

(v) Copper (Cu): Deficiency of copper has been reported in chicks. Too much molybdenum or iron may also decrease its availability. Dietary supplementation of Cu is thus required. The deficiency symptoms are:

Chicks: Bone disorder, lameness, anaemia, depigmentation of feather, abnormal feather growth. Deficiency in egg causes defects in blood and circulatory system and embryonic mortality is increased during second and third days.

Distillery by-products, fishmeal, liver meal, oil cakes and dried whey are the natural feed sources, while supplementary sources are copper sulphate (25% Cu), cupric carbonate (53% Cu) or cupric oxide (75% Cu).

Requirements: 8-10 mg per kg diet.

(vi) Sodium chloride/common salt: It is important for deficiency as well as toxicity. It is a limiting mineral in feedstuffs of plant origin. The deficiency symptoms are Decreased growth and feed intake, high mortality and nervous symptoms in chicks and decreased egg production, poor growth and cannibalism in layers. Common salt is the cheap source of sodium and chloride. The requirement of salt or sodium chloride is 0.30% of diet.

Toxicity: Too much salt in feed or water causes salt toxicity or salt injury characterized by reduced growth, excess water intake, watery droppings, wet litter condition, oedema in abdominal cavity, enlarged kidney, pale colouration of kidney and mortality.

(vii) Selenium (Se): As component of enzyme glutathione peroxidase, it plays important role as antioxidant. It acts in cytoplasm and helps to remove free radicals. Usually Se deficiency does not occur in chickens. It is closely associated with vitamin E and one can spare the other. Deficiency causes exudative diathesis and white muscle disease or muscular dystrophy. Its excess intake causes toxicity.

(F) Public Health Significance: Poultry products are an important part of the human diet and supply highly bioavailable forms of nutrients. Levels of vitamins and minerals in meat and eggs are highly dependent on the levels in the diet. Birds fed diets that are deficient in vitamins or minerals do not supply intended levels of nutrition to human consumers. In fact, the vitamin and trace mineral qualities of poultry products are often optimized at levels that are above the requirement for the animal. Animals deficient in nutrients are often immunocompromised, resulting increased incidence of infectious diseases and, in some cases, evolution of more pathogenic disease organisms. Often animals can serve as buffers for high levels of minerals or other nutrients found in plants and other foodstuff’s, thereby reducing human exposure to potentially toxic nutrients including some heavy metals. However, levels of some nutrients (e.g., selenium, iodine, copper, fluoride, and vitamin A) may accumulate in meat or eggs to levels that might adversely affect human health. Prompt diagnosis and correction of toxicities is important for safeguarding the human food supply.