Animal Nutrition


Biology - 5090

Animal Nutrition

Animal Nutrition
A balanced diet is a diet that provides all the nutrients in the correct amounts needed to carry out life processes. 

Effects of Age, Sex, and Activity

on Human Dietary Needs


As an infant, a child needs as many nutrients as possible. Breast milk is the best option for kids because it provides all extra immune building properties, necessary calories, and fats. As a child grows into toddlerhood, they become active. This will increase their calories, proteins and calcium needs. As for adults, nutritional requirements do not change greatly, except for pregnancy and breastfeeding. 


A pregnant woman with an adequate diet needs no extra food. Her body’s metabolism will adapt to the demands of the growing baby. If her diet is deficient in some nutrients, she will need to increase the intake of those substances. The baby needs proteins, calcium and vitamin D, and iron. 


The production of milk makes a large demand on the mother’s resources. Her metabolism will adjust to these demands if her diet is already adequate. Otherwise, she may need to take in more proteins, vitamins, and calcium.


In most cases, men and women require similar nutritional proportions, but there are exceptions. Women tend to have lower calorie needs because they carry less muscle. Women should eat more nutritional-dense food e.g. complex carbohydrates. Calcium should be consumed in higher amounts by women as they have higher chances of Osteoporosis i.e. fragile bones. Men should at proper nutritional carbohydrates. 


An athlete has different nutritional requirements compared to that of a worker. Exercise improves metabolic efficiency in some people and increases nutrient requirements.  

Principal Sources and Dietary Importance

of Food Types

Food Type

Principle Sources


Crop plants (rice, wheat, potatoes), Fruits, Vegetables, Milk
They give the energy for respiration
Dairy products, Nuts, Avocadoes, Seeds, Fish
They provide energy for our bodies and support for cell growth. They protect organs
Seafood, Meat, Dairy products, Beans, Lentils
They help in the growth and repair of cells and tissues
Vitamin C & Vitamin D

Vitamin C: Citrus Fruits, Leafy Vegetables

Vitamin D: Organ meats, Eggs, Dairy products, Sunlight

V-C helps in preventing cell damage and reduces some diseases. They also help in healing cuts. V-D boosts your immune system and strengthens bones. They increase the absorption of calcium and phosphates.  
Red meat, Beans, Cereals, Fruits, Dark leafy vegetables
It forms an integral part of hemoglobin.
Dairy products, Fruits, Leafy greens, Seafood
It helps in the development of bones, teeth and the body.
Fiber (Roughage)
Cereals, Fruits, Vegetables, Lentils
It helps in the proper functioning of the digestive system and weight management. It also maintains cholesterol levels.
Fruits, Vegetables, Meat, Eggs
It helps to get rid of waste materials.

Vitamin C: 

Lack of vitamin C causes scurvy. It leads to tiredness, anemia, gum disease, and skin problems.

Vitamin D: 

You can get vitamin D through sunlight and organ meat. Lack of vitamin D causes bowing of legs, known as rickets. It also causes the softening of bones, known as degeneration. 


Iron, found in red meat, fruits, and vegetables, is a very important component to make hemoglobin. Lack of iron causes hemoglobin synthesis. This results in nutritional anemia. 

Lack of protein causes a swollen abdomen, known as Kwashiorkor. It is most common in the areas where there is famine or limited food supply. It also causes loss of weight, known as marasamus.


Malnutrition can be defined as a lack of proper nutrition that causes health problems. There are several effects of it, as mentioned below.

i. Starvation: It is a severe lack of nutrition. It causes a lack of concentration, a drop in metabolism, and can even cause further organ damage.

ii. Constipation: When waste materials move too easily through the digestive tract, causing it to become dry and hard.

iii. Coronary heart disease: As a result of plaque buildup in the coronary arteries, there will be a blockage. Arteries will become narrow and rigid, and this restricts blood flow.

iv. Obesity: Lack of energy balance, inactive lifestyle, genes, and lack of sleep lead to obesity.

v. Scurvy: Lack of vitamin C causes scurvy. Vitamin C makes a substance, known as collagen which helps in the repair of various tissues.


protein (Biuret test)
Starch (Iodine in potassium iodide solution)
fats (Ethanol emulsion test)
reducing sugars (Benedict’s solution)

Human Alimentary Canal


Taking in substances into the body through the mouth.

Mechanical Digestion: 

Breakdown of food into small particles without any chemical change to the food molecules.

Chemical Digestion: 

The disintegration of large, insoluble molecules into smaller, soluble molecules.


Movement of small food molecules and ions through the wall of the intestine into the blood.


It is the movement of absorbed food molecules into the cells of the body.


Passing out of food that has not been digested or absorbed (feces) through the anus.

Regions of the Alimentary Canal

Region of the Alimentary Canal


Ingestion of food; Mechanical digestion through teeth; Chemical digestion of starch by amylase; Secretes enzyme
Salivary glands
Produce saliva containing amylase, which is required for chemical digestion of starch
It moves the ingested food to the stomach by peristalsis. No digestion takes place here
Produces gastric juice which has pepsin, which is used for chemical digestion of protein; Produces hydrochloric acid to kill bacteria
It carries out chemical digestion of proteins, fats, and starch; It also gets bile for the emulsification of fats
The digested food is absorbed into the blood and lymph
Secrete pancreatic juice into the duodenum
Produces bile; Deamination of amino acid takes place in the liver
Gall bladder
Stores bile


It absorbs water and bile salts
It stores feces
It is responsible for the Egestion of feces

Mechanical Digestion

It is the breakdown of food into smaller molecules without any chemical change to the food particles. This is done by teeth, through a process known as Mastication.

Incisors are chisel-shaped. 8 of them are present in our mouth. They have 1 root and no ridges. They are used for biting and cutting off pieces of food.

Canines are sharper than the incisors. They have 1 ridge and are used for holding and tearing the food apart. There are 4 of them in our mouth. The molars and premolars have similar functions. They are used for crushing and grinding the food particles. Premolars have 1-2 roots and 2-4 ridges, while the molars have 3-4 roots and ridges.

Figure (i) Human teeth, Credit:

Structure of the Human Tooth

The top, visible part of the tooth is called the crown, while the bottom part is known as root. The gums overlay the jaw. Enamel is the shiny, hard outer shell that covers the crown. Beneath the enamel is the dentine. The dentine is the substance that makes up the tooth. It contains a pulp cavity, which has blood, lymph vessels, and nerve fibres. It supplies nutrients to the dentine. Cement is the tissue covering the surface of the root. It fixes the teeth. 
Figure (ii) Teeth, Credit: wikipedia

Dental decay

There are bacteria present on the surface of our teeth. Food deposits and bacteria form a large layer of plaque. Bacteria in the plaque may affect the gums. They feed on sugars present in the food, producing acid. The acid will dissolve the enamel, forming a hole. The dentine underneath the enamel is softer, thus dissolves more rapidly. If the hole reaches the pulp cavity, bacterial infection can get to the nerve, resulting in tooth decay.

Dental care

Avoid foods with high sugar content.
Make sure to brush your teeth twice a day, and also make use of dental floss.
Regular checkups at the dentist.

Chemical Digestion


Site of Action




Mouth, Duodenum
Slightly alkaline
Maltose, Glucose
Stomach, Duodenum
Acidic in the stomach, Alkaline in the duodenum
Amino acids
Fatty acids, Glycerol

The Mouth

Saliva is a digestive juice that lubricates the food. The salivary gland produces a special enzyme, known as salivary amylase. This works on pH 8. It digests starch into maltose. Maltose breaks down into its monomers in the other part of the body. This semi-digested food is known as a bolus. The bolus is passed to the oesophagus through the food pipe.


The Oesophagus connects your mouth to your stomach. Food moves through a wave-like contraction into the stomach, known as peristalsis. Circular and longitudinal muscles work together but opposite to each other. These are antagonistic pairs. In front of the bolus, circular muscles relax and longitudinal muscles contract. Behind the bolus, longitudinal muscles relax and circular muscles contract.


Pepsin is a protease enzyme produces in the stomach. It requires a low pH to function, which is why the stomach produces hydrochloric acid. The bolus reaches the stomach and lets the walls secrete gastric juices. The hydrochloric acid lowers the pH (2-3). It also denatures enzym3w in harmful microorganisms in food and gives the optimum pH for pepsin activity. It stimulates the digestion of protein through the protease enzyme. It will be partially digested, and this partially digested food is known as a chime. 

Small Intestine

The sphincter is a circular muscle. When it is released, it allows materials to pass through the opening. When contracted, it closes the opening. The food passes from the stomach to the small intestine when sphincter opens. The small intestine is 6 meters long and highly coiled up in the abdominal cavity. In the duodenum, major digestion takes place. It has glands (lining), and it produces three different types of juices (Intestinal juice from itself, bile from the liver, and pancreatic juice from the pancreas). The chime enters the duodenum, which is the first part of the small intestine.

Bile: The liver, situated above the small intestine, secretes bile. Bile is stored in the gall bladder and is poured into the intestine through the bile duct. It is an alkaline juice that neutralizes the acidic mixture of food and gastric juices entering the duodenum from the stomach to provide a suitable pH for enzyme action. Bile also emulsifies fats to increase the surface area for the chemical digestion of fats to fatty acids and glycerol through the enzyme, lipase.

Pancreatic juice: Pancreas secretes the pancreatic juice which pours into the gall bladder. Emulsified lipids in the pancreatic juice into pancreatic lipase to fatty acids and glycerol. Semi-digested starch is digested by pancreatic amylase. As a result, it produces maltose.

Intestinal Juice: This is secreted by the small intestine. It contains an enzyme, known as intestinal lipase, which changes into fatty acids and glycerol.


The small intestine is the region where this process occurs. The adaptations of the small intestine are as following:

Small intestine cells are changed into villi and microvilli, which are finger-like projections.

Villi increase the surface area required for absorption. 

6 meters long

It contains blood capillaries to carry away the absorbed food molecules.

They have a thin foiled lining for easy movement of food molecules.

Structure of Villus

In each villus, there are two types of capillaries present: Lacteal and blood. The lacteal capillary is a lymphatic capillary which absorbs fatty acids. Blood capillaries absorb all amino acids, glucose, mineral salts and water.

Large Intestine

Water and mineral salts mostly dissolve in the large intestine. Undigested food (fibre/cellulose) is stored in the rectum for a certain period and comes out as faeces. The fibre helps in peristalsis. Faeces moves from rectum Anus is the opening of the rectum. The act of removing the faeces from the body is known as Egestion.


It is the loss of watery feces. When you contaminated food, water does not dissolve in blood, causing a problem in the intestine. Therefore, faeces become thin and watery. It can be treated by Oral Rehydration Therapy (ORS), which is a fluid replacement strategy used to treat dehydration caused by diarrhea.


Cholera is a disease caused by a bacterium, Vibrio Cholerae. Intake of contaminated food or drink can cause this disease. The bacterium produces a toxin that causes the secretion of chloride ions into the small intestine. Thus, water goes into the large intestine with feces. This causes the osmotic movement of water into the alimentary canal. This leads to diarrhea, dehydration, and loss of mineral salts from the blood.

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