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Animal Nutrition

About Animal Nutrition

Animals are not able to synthesize their food, therefore they depend on ready-made food for their nutritional requirements. The term nutrition refers to the total of all the processes related to the conversion of the raw foodstuff into the stuff of the body to supply energy for different metabolic activities and also for the repair and growth. In another word, we can define nutrition as the process by which an organism derives energy to work and other materials, required for the growth and maintenance of the various activities of life.

Food intake: Different organisms obtain food in different ways but carry out similar chemical reactions to utilize it. To take food, protozoans use pseudopodia, flagella or cilia; sponges and mussels, a current of water; Hydra, tentacles beset with stinging cells; planarians and earthworms, a muscular pharynx; flukes and leeches, oral sucker; insects and other arthropods, mouthparts of various kinds; and seastars and sea urchins, tube feet. Sharks capture prey with the jaws; frog and lizard with the tongue; birds with beaks of sorts; rabbit and hare use forepaws, lips and teeth; cattle, lips, and teeth; carnivores, claws, and teeth; giraffes, tongue; elephants, proboscis (trunk); humans, monkeys, and apes use hands.Do follow NCERT solutions for class 12 biology

Type of Animal Nutrition

  • Autotrophic (Gk. auto = self; trope = nourishment) nutrition: When organisms synthesize the organic nutrients directly from available inorganic substances utilizing energy in any form. Autotrophic nutrition is typical of plants. It is therefore also called holophytic nutrition(Gk.–holos = entire, phyton = plant).

Autotrophic nutrition is of two types :

  1. Chemosynthetic : The primitive autotrophic prokaryotes used chemical (glycolytic) energy to make carbohydrates from H2S and CO2. Present day deep sea sulphide bacteria do obtain food in this way.
  2. Photosynthetic   : Plants or chlorophyll containing organisms utilize solar energy (light) to synthesize food from CO2 and H2O.
  • Heterotrophic     : When organisms derive food from available products prepared by plants. All animals, fungi, bacteria etc. have this mode of nutrition.

Types of Heteroterotrophic Nutrition

Saprotrophic : Food is obtained by absorption through cell or body surface from dead organic material, dead organism’s body etc. If performed by plants it is called saprophytic and if by animals it is called Saprozoic.

Mixotrophic : Euglena represents this type. In presence of light it performs photosynthesis, in absence of light it is saprotrophic. Some species also show holozoic mode of nutrition.

Parasitic : Obtaining food at the cost of other living organisms (host) and causing harm to it e.g., Taenia, Plasmodium, Ascaris, Entamoeba, bacteria, viruses.

Holozoic : Organisms feed on the solid organic food materials. The food may be a whole plant or whole animal or their parts.

Depending upon the source of food, holozoic or holotrophs are of following types



Feeding Habit Term

Feeding On




Flesh of other animals

Lion, dog, cat



Decomposing organic matter




Plant (or vegetation)

Rabbit, cow, horse




Frog, bat



All types of food

Cockroach, human



pThe faeces

Pig, dung beetles



Blood suckers

Leech, mosquito, bed bug, lamprey



Fruit eaters

Monkey, p

Important points about Animal Nutrition

  • Autotrophic nutrition is also called holophytic nutrition (Gk. holos = complete; phyton = plant) or self-nourishment.

  • Holozoic nutrition is also called holotrophic or ingestive nutrition.
  • Digestive gland of prawn is hepatopancreas.
  • Length of small intestine is related to the feeding habits of an animal. It is relatively shorter in carnivores but longer in herbivores.
  • Housefly releases saliva on the food and ingests the liquid and simplified food with its sponging type mouth parts.
  • Palatine rugae : Folds on hard palate. These are large sized in carnivores to grip food during tearing.
  • Tonsils are formed of lymphoid tissue and are the sites of formation of lymphocytes to provide immunity.
  • Degluttition : Swallowing of food bolus. It is partly voluntary and partly involuntary process.
  • Peristalsis : Involuntary movements of gut by which food bolus is moved backward. It is least in rectum of alimentary canal.
  • Pendular movements : Ring-like contractions moving backward and forward over short lengths of intestine to churn and mix the food and digestive juices.
  • Haustrations : Segmenting movement of large intestine which help in absorption of water and minerals so formation of faeces.
  • Upper part (1/3rd part) of oesophagus is, made up of voluntary muscles while its lower 2/3rd part is with smooth muscles.
  • Hump of camel has stored fats. Chemical breakdown of these fats provides water for metabolism during deficiency of water.
  • Villi are most numerous in ileum of small intestine.
  • Appendicitis : Elongation of vermiform appendix due to decay of food or worm infection. Its surgical removal is called appendicectomy.
  • Tusks of elephants are incisors of upper jaw, while tusks of male wild boar and walrus are upper canines.
  • Caecum and vermiform appendix is long sized in herbivores like rabbit, ass and horse as symbiotic digestion of cellulose by bacteria occurs in these parts.
  • Bursa Fabricus : Also called cloacal thymus, is a lymphoid mass in the cloaca of birds. It is site of differentiation of B-lymphocytes so a part fo immune system.
  • Wharton’s duct : Duct of sub-maxillary salivary gland.
  • Bartholin’s duct : Duct of smallest sized sublingual salivary gland.
  • Zymogenic cells are mainly present in the basal part of fundic gastric glands.
  • Liver : Largest gland of body. It is heavier in male (about 1.6 kg in weight) and forms about 1/40th of the body weight. It is largest chemical factory of body.
  • Bile duct is also called Ductus choledochus and is formed by joining of cystic duct from the gall bladder and common hepatic duct from liver lobes.
  • Salivary glands are reduced or absent in whales and sirenians.
  • Poison glands of snakes are modified parotid salivary glands.
  • Viral infection of parotid salivary glands causes mumps characterized by painful jaw movements.
  • Liver of rabbit is formed of 5 lobes : Right central (largest lobe), left-central, left lateral, caudate and  spigelian lobe (smallest lobe). Spigelian lobe is absent from liver of man.
  • Wirsung duct : Pancreatic duct which joins the bile duct.
  • Paneth cells : Found in crypts of Lieberkuhn and secrete enterocrinin hormone.
  • Peyer’s patches : Lymphoid masses in submucosa of ileum and are involved in the production of B-lymphocytes. These are also called abdominal tonsils.
  • Pancreatic amylase is also called amylopsin.
  • Rennin, also called chymosin, is not found in gastric juice of frog.
  • Gastric digestion period depends upon nature of food ingested e.g. about 1-2 hours for a carbohydrate meal; about 3 hours a proteinous meal while 5-6 hours for a fatty meal.
  • Trypsin is called universral enzyme as found from protozoans to mammals.
  • Yellow colour of faeces is due to bilirubin pigment.
  • Heart burn or Pyrosis : Burning sensation of duodenal mucosa due to action of acidic chyme squeezed in duodenum due to incomplete closing of pyloric apertrue.
  • Gastritis : Inflammation of stomach due to excessive intake of alcohol.
  • Protection to intestinal mucosa : Secretion of large amounts of mucus, inactive nature of proteolytic enzymes, release of digestive juices only when food present  in the gut, and glycocalyx coat.
  • Argentaffin cells : Endocrine cells of pyloric stomach which secrete gastrin hormone to stimulate the secretion of gastric juices.
  • Chymotrypsin acts on peptide bonds on C-terminus side of tyrosine, tryptophan and phenylalanine amino acids.
  • A man can survive without food for about  six weeks during which stored foods like glycogen of liver and fats in the adipose tissue are catabolized.
  • Urge for egestion is initiated by stretch receptors present in the wall of rectum which are stimulated by the expansion of rectum.
  • Among the diet, carbohydrates and fats act as energy sources; proteins, salts and water act as body builders, while vitamins and hormones act as regulators.
  • Food production in India has increased from 50.8 million tonnes in 1950-51 to 98.7 million tonnes in 1996-97.
  • Vitamin means vital amines, but all the vitamins are not amines.
  • Most of vitamins are exgogenous and taken along with diet.
  • Vitamins may be lost due to improper cooking or excessive wahsing of vegetables after chopping.
  • IDD-Day (Iodine Deficiency Disorder Day) : 21st October.
  • Most of B-complex vitamins act as coenzymes.
  • Pellagra is also called 4-D syndrome as is characterized by dermatitis, dementia, diarrhoea and death.
  • Baleen – Whale bone whale have in the buccal cavity a special structure called baleen or whale bone. It consists of several parallel horny plates hanging from the palate.
  • Cheek pouches – In some rodents (squirrel, rat) certain old world monkey, the vestibule extends to form cheek pouches for temporary storage of masticated food.
  • Taste buds contain group of sensory epithelial cells. These cells are anteriorly provided with kinocilium and posteriorly with nerve fibres. The taste centres are present in brain.
  • Gustatoreceptor – The organ concerned with taste detection. They are a type of chemoreceptor found in the parietal lobe of cerebrum.
  • In frog, tongue is anteriorly attached with the floor of buccopharyngeal cavity at lower jaw, whereas posterior end is free and bifid.
  • The tongue of snake is bifid and sensitive to odour and vibration.
  • Toothpaste protects the gum, whereas fluorides present in toothpaste clean the apex. The excess of fluorides causes the disease fluorisis which leads to decaying of teeth and bones.
  • Elephant tusk is the upper incisors.
  • 3rd molar in human is called as wisdom teeth as arises after the age of 16-17 years. Wisdom teeth 4 in number.
  • Teeth of fishes are modified placoid scales.
  • Teeth in frog are present only on upper jaw.
  • Caries  Decay of teeth due to degeneration of enamel and formation of cavities.
  • Pyorrhoea infected gums and tooth sockets.
  • Maximum number of teeth present in opossum is 50.
  • The number of teeth that grows once and twice in humans life is 12 and 20 respectively.
  • Lophodont teeth in elephant are premolar and molar.
  • Incisors of rats are polyphyodont.
  • Teeth of sloths and armadillos have no enamel.
  • Enamel is lacking in the teeth of whales.
  • Jacobson organ (Vomeronasal organs) – They are independent chambers below nasal cavities found in most tetrapods, although they are sometimes vestigial (like human). Absent in fish but occurs embryonic rudiments in most vertebrates. In reptiles, they are best developed in lizards, snakes and sphenodon but are absent in adult crocodiles. Jacobsons organ well developed in such animals that hold food in their mouth. This organ serve to smell food and recognize its chemical nature. They also help enemy recognition, locating members to opposite sex, courtship etc.
  • Teeth absent in Bufo and Pipa (Toads).
  • Taste of chilli is not real taste but it is burning sensation of nerves.
  • Fangs of poisonous snake attached to maxillary bones, they are replaceable. Solenoglyphous, Proteroglyphus and Opisthoglyphus types of fang occurs in poisonous snake.

Differences between small and large intestines

Small Intestine

Large Intestine

Longer (about 6 m.) but narrower than large intestine.

Shorter (about 1.5 m.) but wider than small intestine.

Differentiated into duodenum, jejunum and ileum.

Differentiated into caecum, appendix, colon and rectum.

Mucous membrane has plicae circulares and villi.

Mucous membrane is mostly smooth (without plicae and villi). Rectum has longitudinal folds.

Lacks taeniae coli, haustra and epiploic appendages.

Has taeniae coli, haustra and appendices epiploicae.

Peyer’s patches are present in the ileum.

Peyer’s patches not formed, lymphoid nodules beins scattered.

Completes digestion and absorbs digestion products. Also produces some hormones.

Absorbs water, forms and eliminates faeces, produces vitamins Band Kby bacterial activity and excretes certain inorganic ions.

Mucosal irritation due to infection causes diarrhoea.

Mucosal irritation due to infection causes dysentery.

  • Cellulose is digested by the enzyme cellulase synthesized by the microorganisms present in the lumen.
  • Cellulose  Acetic acid + Propionic acid + Butyric acid + Small chain fatty acid.
  • Sacculus rotundus is a dilated sac like structure present in rabbit at the junction of ileum, caecum and colon. It contains ileo-caecal valve, which guides the direction of food from ileum to caecum. Sacculus rotundus is absent in human but ileo-caecal valve is present.
  • The hindgut of all vertebrates (except metatherian and eutherian mammals) includes cloaca and cloacal aperture, instead of anal canal and anus.
  • Cloaca is divided into three parts
  • Coprodaeum is a part of rectum, where faeces are stored.
  • Urodaeum a depression in the part of cloaca where urinary duct and urinary bladder open.
  • Proctodaeum terminal part of cloaca that is common opening for the excretion of urinary, genital and faecal matter and externally open by anus.
  • Digestion of cellulose takes place in caecum of rabbit with the help of enzyme cellulase produced by symbiotic microorganism. Cellulose digestion does not occur in human.
  • Peyer’s patches in the intestine are the site of production of B-lymphocyte.
  • In most of the vertebrate's protein digestion ends in ileum.
  • The study of alimentary canal is called Enterology.
  • Auerbach’s plexus is present in small intestine.
  • Digestion of cellulose is also found in termites (white ants). In which symbiotic flagellate Triconympha found in their intestine that secretes enzyme β-glucosidaes which hydrolyse the cellulose to sugars which are used by both symbionts.
  • Bursa fabricus is also called cloacal thymus, is a lymphoid mass in the cloaca of birds. It is site of differentiation of B-lymphocytes. So a part of immune system.

Summary of chemical digestion of food

Chemical digestion of protein

Chemical digestion of carbohydrates

Chemical digestion of fats

Chemical digestion of nucleic acid

Protein Food



       (gastric juice)


Proteoses and Peptones

Trypsin and


(pancreatic juice)


Tri and Dipeptides


(intestinal juice)


Amino acids








 (pancreatic juice)





  Maltase, Lactase


 (intestinal juice)



(glucose, fructose,  galactose)



    Bile salts



Emulsified Fats


(pancreatic and                     

intestinal juice)


Fatty acids

and glycerol

Nucleid acid

(DNA and RNA)

    Pancreatic nucleases

    (DNAase & RNAase)




     Nucleotidases and                     



Nitrogen bases

Pentose sugars and inorganic phosphate


Differences between diffusion and active transport



Active transport

It is a physical process.

It is a vital process.

It moves small nutrient molecules across the cell membranes only down the concentration gradient.

It moves small nutrient molecules across the cell membranes independent of concentration gradient (both down and against).

It does not use carrier protein molecules in moving materials.

It uses carrier protein molecules in moving materials.

It does not utilize energy.

It consumes energy derived by hydrolysis of ATP.

It is a slow process.

It is a rapid process.

No material can be fully absorbed by diffusion.

Materials can be fully absorbed from the intestine.

Summary of physiology of digestion

Major gastrointestinal enzyme in mammals

Name of gland

Name of digestive juice & optimum pH

Name of enzyme

Site of action



Salivary glands

Saliva (6.8)

Ptyalin / Salivary amylase


Starch, dextrins, glycogen

Dextrins, maltose, isomaltose and limit dextrin.

Gastric glands

Gastric Juice (1-3)



Proteins, casein (Milk)

Peptones, paracasein (curd).






Gastric lipase



Fatty acid and Glycerol.

Bile juice


No enzymes



Makes the food alkaline, emulsifies fat and kills the harmful bacteria.


Bile ( 7.7 – 8.0)

No enzyme  but useful digestive juice, provides alkaline medium, stops the action of HCl. Emulsifies fats and kills – harmful bacteria.


Pancreatic Juice          (7.3 – 8.6)


Small intestine


dextrins, glycogen.

‘Limits’ dextrins, maltose, isomaltose.


Small intestine

Proteins, Chymotry-psinogen (inactive) procarboxy pept- idases (inactive) Fibrinogen (blood) Casein (milk)

Peptides, Chymotrypsin (active) carboxy pepti-dases (active) Elastase (active), Fibrin (clot) Para-casein (curd)


Small intestine




Small intestine


Smaller peptides and Amino acids.

Lipase / Steapsin

Small intestine


Mono-glycerides, fatty acids

DNA ase

Small intestine



RNA ase

Small intestine



Intestinal glands

Intestinal Juice


Enteropeptidase (enterokinase)

Small Intestine

Trypsinogen (inactive)

Trypsin (active)


Small Intestine


Smaller peptides and amino acid


Small Intestine

Dipeptides ‘Limit’ dextrins

Amino acids


Small Intestine




Small Intestine




Small Intestine


Glucose, fructose


Small Intestine


Glucose, galactose


Small Intestine


Monoglycerides, fatty acids


Small Intestine


Nucleosides, inorganic phosphate

Nucleoside       Phosphorylases

Small Intestine

Nucleosides phosphate

Purine, pyrimidine, pentose, phosphate

Differences between caloric fuel value and physiological fuel value



Caloric fuel value

Physiological fuel value

Site of production

Energy in kcal produced by the complete combustion of 1 gm. of substance in a bomb calorimeter.

Energy in kcal produced by the oxidation of 1 gm. of substance in the body tissues.

Amount of energy

1 gm. of carbohydrates provide 4.1 kcal. of energy.

1 gm. of carbohydrates provide 4.0 kcal. of energy.

Fat soluble vitamins


Name of vitamins and chemical formula



Daily requirement per day


Name of Deficiency Disease


Other Features

Vitamin A or

Retinol or anti xero-phthalmic or anti infection vitamin

Fat soluble vitamins

Mc-Collumn and Davis (1913)

Vegetables butter liver oils egg yolk, mango and orange, carrot.

2 mg

Part of visual pigment, maintenance of epithelia and prevention of keratini-zation of epithelium.

Xerophthalmia Night blindness or nyctalopia Keratomalacia.


  • Drying of eyeball

  • Unable to see in dim light

  • Epithelium keratinised

  • Dry scaly skin

Synthesized and stored in the liver.

Destroyed by - strong light.

Vitamin D or

Ergocalciferol        or sunshine vitamin or anti rachitic vitamin


Steenbock and Hess 1924)  

Cod liver oil, butter, fish, eggs, milk, brain, lung, and spleen.

0.01 mg

Facilitates absorption of calcium and phosphorus by intestine and their retention in body and deposition in bones.

Rickets  in children

Osteomalacia in adults.

Deformities of bones like bowlegs pigeon chest

Weak bones liable to easy fracture

Synthesized in the body on exposure of skin     (7-hydroxy cholesterol)

to light.

Destroyed by – oral contraceptives

Vitamin E or

α Tocopherol

or anti sterility vitamin


Evan and sore (1922)

Fresh green vegetables, meat, yolk, vegetable oils, butter and cheese, peanuts

20 mg

Antioxidant and some role in ETS.



Muscular atrophy

Destruction of RBC.

In male causes sterility and in female abortion may occur of offspring. Effect not proved in man.

Degeneration of muscles

Destroyed by UV – rays.

It is also used for curing tumour and cancer

Vitamin K or

Phylloquinone or

anti haemorrhagic vit-amin

nutrition for animals

Dam and Droisy (1935)

Fresh green vegetables. to matoes, liver, soyabean, cheese, egg.

0.07 – 0.14 mg

Synthesis of prothrombin for normal clotting of blood.


Reduced ability of blood to clot and also leads to haemorrhages.

Vitamin K is synthesised by intestinal microbes present in the intestine.

Destroyed by–prolonged use of antibiotics.

Water soluble vitamins


Name of Vitamins and Chemical Formula





Name of Deficiency Disease


Other Features

Vitamin Fat soluble vitamins or Thiamine or anti neuritic or antiberiberi

Fat soluble vitamins

C. Funk (1926)

Branrice, whole wheat flour, egg, meat, liver yeast etc.

1-1.5 mg

Act as co-enzyme in cellular respiration, role in nutrition of nerve cells.

Essential for carbohydrate metabolism, protein synthesis and control water balance in body.

Beri- beri – or Dry beri - beri (man)

Polyneuritis or  (animals) wet beri - beri     

Cardiovascular atrophy

Loss of appetite and weight, retarded growth, muscular dystrophy.

Nerves to become extremely irritable.

Heart enlargement

Beri-beri disease was discovered by Eijkman

Destroyed by – cooking

Vitamin animal nutrition or G or yellow enzyme or   Riboflavin or Lactoflavin or ovaflavin or hepatoflavin animal nutrition

Warburg and Christain

Cheese, egg, yeast, meat, liver, cereals, green, vegetable.

1-2 mg

Required for cell growth.

Form pair of coenzyme (FMN, FAD).




Cracking of skin at corners of mouth

Inflammation of tongue

Inflammation of skin

Stored in liver, Excess of this is eliminated in urine.

It is associated with the physiology of vision

Vitaminanimal nutriotion

Yeast factor or pantothenic acid or anti graying factor on chick antidermatitis factor  animal nutriotion

Williams (1933)

All foods, more in yeast, kidney, liver, egg, meat, milk, ground nut

5-10 mg

Part of co-enzyme A. needed for cell respiration, necessary for normal skin and nerves.

Burning feet syndrome,

Nervous disorder

Nerve degeneration

It occurs in all types of plants and animal tissues.

Its deficiency cause graying of hair

Vitamin animal nutriotion or Niacin or Nicotinic acid or pellagra preventing factor

animal nutriotion

Goldberger (1912)

Fresh meat, liver, fish, milk, cereals, pulses, yeast etc.

16-20 mg

It is an essential component of NAD and NADP thus form coenzymes, metabolism of carbohydrates, functioning of gastrointestinal tract and nervous system






(4-D syndrome)

Rough skin

Inflammation of skin which becomes scaly and papillated


Neural deterioration which may lead to madness  

It is characterised by 3D’s i.e. dermatitis diarrhoea and dementia

Destroyed by – cooking

Pellagra preventing factor Goldberger also called Goldberger’s p-p factor

It is also synthesized by colon bacteria

Vitaminanimal nutriotion or pyrido-xine or Rat anti dermat-ities factor

animal nutriotion

Gyorgyi (1928)

Brewer’s yeast, liver, egg, yolk, kidney, milk, and vegetables.

2 mg

It is essential component of coenzyme pyridoxal phosphate. It promotes growth in rats used for curing tuberculosis.


Dermatitis, paralysis & death of rats.

Mental disorder



Nausea, lack of RBC (blood)

Disturbance of  central nervous system

Skin leisons

Term animal nutriotion was coined by Gyorgy.

Destroyed by – cooking and oral contraceptives  

Vitamin H oranimal nutriotion or Biotin or coenzyme R  or Avidin

animal nutriotion

Bateman and Allison (1916)

Yeast, vegetables and egg yolk

150-300 mg

It acts as coenzymes and essential for fat synthesis and energy production.


Scaly and itchy skin

It is synthesized by intestinal bacteria Destroyed by – prolonged use of antibiotics  

Folic Acid or  Vitamin M or folacin or Anti anaemic factor

Day (1935)

Green vegetable (spinach) Banana, orange and Liver.

0.4 mg

It forms coenzymes and play essential role in cell metabolism, Necessary for erythropoiesis, required for DNA synthesis.

Megaloblastic anaemia.


Enlarged RBCs

Ulceration of mouth

It is also synthesized by intestinal bacteria

Destroyed by - cooking

Vitaminanimal nutriotion

or Cyanocobalamine or Animal protein factor (APF) or Intrinsic factor of castle


Rickets (1948)

Meat, egg, liver, fish, synthesized by intestinal bacteria.

0.003 mg

Required for chromosome duplication and formation of blood corpuscles.

Pernicious anaemia

Reduced formation of erythrocytes in bone marrow

It is also known as anti pernicious factor

Also synthesized by intestinal bacteria in human colon

Destroyed by – excessive heat

Vitamin C or Ascorbic Acid

animal nutrition

Szent Gyorgyi (1928)

Citrus fruits such as lemon, mango, amla, plumes, guava.

40-60 mg

Functions as part of oxidation-reduction system.

Helps in secretion of collagen cement dentine.

Helps body to develop resistance to diseases.

Helps in absorption of Ca and Fe in the intestine.

Wound healing.



Spongy and bleeding gums, fragile blood vessels and bones.

Required by primates, all other vertebrates and some other invertebrates can synthesize vitamin C. It is the earliest known vitamin.

It is wound healing vitamin. Destroyed by – Heating



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