Feed can be described as the materials which give nourishment to
animals. The components of a feed which are capable of being
utilized by the animal in life support functions are called
nutrients. Nutrients may also be defined as a specific element or
compound derived from ingested food and used to support the
physiological processes of life. Nutrients are required for normal
body functions such as digestion, respiration, blood circulation,
locomotion, reproduction etc.
The major nutrients found in dairy animal feed are water,
carbohydrates, proteins, minerals or ash and vitamins.
Water is the most abundant, the cheapest but the most important
nutrient. Its importance can be estimated from the fact that life
cannot exist without it and adult animal’s body contains 70-80% water.
Moreover animal product such as milk contains a large amount of
water (upto 83 to 87%).
Functions of Water:
It is an essential part of all body
It helps in maintenance of body
temperature and pH
It helps in digestion, absorption
It helps in respiration by
It helps in the transportation of
nutrients to different parts of the body
It acts as solvent for many
constituents of body nutrients
It protects the various vital
organs against outer shocks and injuries
It acts as a cushion for tissue
cells and nervous system
It provides shapes to the body
It maintains proper
fluid and ion balance in body
All the biochemical and
physiological reactions take place in water
Sources of Water in Animals:
There are three sources of water:
Drinking water which is the major
portion of water consumed by an animal
Feed water which reaches the animal
body along with feed. For example green fodder contains 75-95% moisture
Metabolic water which result from
the metabolic activities of various nutrients present inside the
animal body. For example one gram carbohydrates, one gram fat
and one gram protein yield 0.60 ml, 1.70 ml and 0.42 ml
metabolic water respectively.
Carbohydrates are compound of carbon, hydrogen and oxygen in which
the ratio of hydrogen to oxygen is almost the same as that in water.
Carbohydrates may be defined as polyhydroxy aldehyde or ketone or
anhydrides of such derivatives. These are synthesized in plant
through photosynthesis. Plants tissue may contain carbohydrates up
to 50% of its dry weight in forages and about 80% in cereal grains.
Classification of Carbohydrates:
Carbohydrates are divided into three main groups:
– Monosaccharides are simple sugars which cannot further be hydrolyzed.
They are the building block of more complex carbohydrates. They may
be subdivided into trioses (having three carbons), tetroses (having
four carbons), pentoses (having five carbons), hexoses (having six
carbons) and heptoses (having seven carbons). Glucose, fructose,
mannose and ribose are the examples of simple sugars.
– Disaccharides are compound sugars which are composed of two monosaccharides. These mononsaccharides are connected through
glycosidic linkage. Sucrose, maltose, lactose and cellobiose are
the examples disaccharides.
– Polysaccharides are complex sugars which contain a large number of monosaccharides. These are not sweet in taste that is why also
called as non sugars. These are further classified as structural and
non structural carbohydrates.
- Most of the cell wall in plant is composed of structural
polysaccharides in the form of cellulose and hemicelluloses. These
polysaccharides provide structural support for plant tissue. Like
starch, cellulose and hemicelluloses are also made of glucose units
but are less digestible due to complex linkages among the glucose
units. The structural carbohydrate content increases with the
maturity of plants.
Non structural polysaccharides
- Starch is one of the most important non structural and non fibrous
polysaccharide found in plants, particularly in grains ad tubers.
Most of the plant glucose is stored in the form of starch. Starch
contains amylose and amylopectin in variable concentrations. Starch
from different sources varies in its digestibility.
Functions of Carbohydrates:
They are the source of energy for
They are building stones for other
They are stored in animal body in
form of glycogen
They give the filing effect to
Lipids are organic compounds which are soluble in organic solvents
and have important biochemical and physiological functions in body.
Nutritionally important lipids are fats and oils. The building
blocks of lipids are fatty acids and glycerol. Depending upon the
number of fatty acids present in lipids they are classified as monoglycerides, diglycerides, and triglycerides. Fats are solid at
room temperature while oils are liquid at room temperature. Waxes
are esters of fatty acids with alcohols other than glycerol.
They supply energy
They provide heat insulation and
protection from minor injury
They are source of essential fatty
They carry fat soluble vitamins
They play role in structural
Proteins are complex organic compounds which are made up of amino
acids. Like carbohydrates proteins are composed of carbon,
hydrogen, oxygen, but in addition nitrogen is also present. Some
proteins also contain sulphur, iron and phosphorus. Proteins are
found in large amount in muscles, cell membrane, skin, wool/hair,
hormones and enzymes. Plants and some bacteria are the original
sources of all proteins because they have ability to synthesize
their own proteins.
Amino acids present in protein are associated with each other by
peptide linkages. The type of amino acids present in protein
molecule and their relative proportion and arrangement are unique
for each protein. Nutritional value of protein depends primarily on
its amino acid composition. From nutritional point of view amino
acids are grouped as essential and non essential amino acids.
Essential amino acids are those, which body cannot synthesize and
they are required to be supplied in the diets. So they are dietary
essential. On the other hand non essential amino acids are those
which body can synthesize through transamination. Essential amino
acids include threonine, valine, histidine, arginine, lysine, leucine,
isoleusine, methionine, phenyalanine, and tryptophan. Non essential
amino acids include hydroxyproline, proline, alanine, serine,
cystine, gycine, glutamic acid, aspartic acid, tyrosine, and
Functions of Proteins:
They have role in formation of body
structure and tissues
They have regulatory function as
osmotic pressure, water balance and pH
They are necessary for body
hormones and enzymes
They are required for milk
They are involved in hereditary
They play role in antibodies
formation to develop immunity in body
Minerals are essential dietary constituents which are required in
relatively small quantities. Animal tissue and feed contain about 45
mineral elements in varying quantities. On the basis of requirement
minerals are classified as micromineral and macromineral.
Macrominerals are those which are required in relatively large
amounts while micro minerals are those which are required in small
amount. Microminerals are also called trace elements. Calcium,
phosphorus, potassium, sodium, chlorine, magnesium and sulphur are
the examples of some macrominerals while iron, zinc, manganese,
copper, cobalt, iodine, selenium, chromium and molybdenum are the
examples of some microminerals. Animal body contains 3-5% minerals
on empty body weight basis.
Functions of Minerals:
They give rigidity and strength to
They are components of certain
biomolecules such as proteins, phospholipids, mucopolysaccharides, hormones and vitamins
They also act as activator of many
As soluble salts, they play an
important role in osmosis, acid base balance, muscle contraction
and nerve transmission
Mineral status of animal also
affects the balance of symbiotic microflora of gastrointestinal
tract, modulates immunity and helps the animals against stress.
Vitamins are complex organic compounds that are essential for life
and good health. These are classified as fat soluble vitamins and
water soluble vitamins. Fat soluble vitamins include A, D, E and K
while water soluble vitamins are thiamin (B1), riboflavin (vitamin
B2), niacin (vitamin B3), pantothenic acid (vitamin B5), pyridoxamine
(vitamin B6), cobalamin (vitamin B12), choline, folic acid and
ascorbic acid (vitamin C).