Carbohydrates are a characteristic of plants – a large portion of the dry matter of plants consists of carbohydrates, cellulose and lignin.

With animals, it is different; carbohydrates are present in very small amounts in the animal body. They are energy foods and therefore shortly after digestion are used as a source of heat and energy.

Carbohydrates consist of three elements only; namely:

  • C = Carbon
    • H = Hydrogen
    • O = Oxygen

These three elements can be combined in many different ways, and they are grouped according to the number of carbon atoms in the molecule, and the complexity of it.

MoPCIccharides: These are the simplest sugars, glucose being one of them.

Glucose is one of the first carbohydrates to be formed during photosynthesis, and it is also the principal substance into which more complex carbohydrates are broken down when digested.

Should an animal require an immediate source of energy, glucose can be given as a drink or injected into the blood. An example of this is Calcium Boroglucose which can be injected into a cow suffering from Milk Fever. This provides both calcium and glucose.

A very important sub-group of the MoPCIccharides are the Cyanogenic Glycosides.

When these substances come into contact with water, hydrogen cyanide (HCN) can be produced, and is an extremely poisonous substance. Examples of foods which can produce this poison are:

Star grass pastures, particularly those which have been heavily fertilized.

  • Linseed
    • Jackbean
    • Stones of Peaches and Plums.

Disaccharides: These are more complex sugars:

  • Sucrose: Common sugar used in the home.
    • Lactose: Milk sugar.
    • Maltose: Malt sugar.

These sugars when digested are broken down to simple moPCIccharides and are then available to the animal as a source of energy.


These are the most complex of all the sugars or carbohydrates. Although they are composed of moPCIccharides, and disaccharides, they bear little resemblance to them.


This is the main energy reserve in plants and is an important member of this group.

Cellulose: is the main material of cell walls.

Lignin: this is the hard outer surface of grass, trees etc.


Carbohydrates are burnt up in the presence of oxygen to produce energy, carbon dioxide and water. This process takes place in the cells of the muscles and other organs. The energy produced is used by the animal either in the form of heat or in movement, growth, reproduction, and other bodily functions. The carbohydrates and oxygen are carried to the cells by the arteries of the blood system and the carbon dioxide and other waste products are carried away from the cells by the veins. The whole process is known as Respiration and can be shown in the following equation:

  • Glucose + Oxygen = Carbon Dioxide + Water + Energy
    • C6H12O6   +    602      = 6 C 02          + 6H20 + Calories


Very little carbohydrate is stored as such in the body. Excess glucose is converted into the carbohydrate called glycogen and this is stored in the liver where it acts as a reservoir which can be converted back into glucose and fed into the bloodstream when required. However, only a comparatively small amount of glycogen can be stored in the liver. Additional carbohydrate is normally converted into fat which is stored under the skin, inside the muscles, and around certain organs of the body such as the kidneys. At the end of this lecture, there is a list of the various areas in the body where fat is stored.


The fattening of animals on the farm, particularly cattle and pigs, is carried out largely by the feeding of carbohydrate. Extra carbohydrate is fed to the animal so that it can be converted into fat and stored. The amount of this extra carbohydrate has to be very carefully calculated so that the animal is well finished and not over-fat. This, again, is particularly important with cattle and pigs, because animals which are too fat are given lower grades; this means that the farmer receives less money for them.


All feeds fed to farm animals contain carbohydrate, but the most carbohydrate is found in the concentrate feeds. All cereals, maize, barley, wheat, oats and rye are high in carbohydrate and low in protein. Oil seeds and oilseed cakes are high in carbohydrate and also high in protein. Root  crops and particularly potatoes are high in carbohydrate and low in protein. Grass, both veld grass and pasture grass is high in carbohydrate, but much of this is in the form of cellulose that can be utilised only by ruminants.

Concentrate feeds that are high in carbohydrate are called high energy feeds because the carbohydrate in it provides a lot of energy to the animal, once it has been digested. Maize is a good example of a high energy feed because the maize grain is composed mainly of the carbohydrate starch, and this can be easily broken down by both the ruminant and non-ruminant to provide a good source of energy to keep the animal going or to store as fat.

  • FATS

Fats and oils can be grouped together under the common name of lipids. The difference between a fat and oil is that a fat is solid at normal temperatures whereas oil is liquid. They are made up of carbon, hydrogen and oxygen but the amount of carbon and hydrogen is much higher in fats than in

carbohydrates; because of this, lipids have a higher Energy Value than Carbohydrates. This means that they provide more heat and energy when digested by the animal than do carbohydrates – about 2 1/4 times as much.

Lipids occur widely in both plants and animals, and in animals, fats are the main reserve of energy.

Grazing animals build up reserves of fat during the summer when there is plenty of food in the form of grass, and they draw on these reserves during the winter when the quality of the grazing is much poorer. When animals lose weight during the winter, this is because they have used up any fat that has been stored in the body.


Adipose: (especially of body tissue) used for the storage of fat.  
Unthrifty: (of livestock or plants) not strong and healthy.  
Oblique: neither parallel nor at right angles to a specified or implied line; slanting.

Fats and oils are made up of glycerol and fatty acids. Glycerol is commonly known as glycerin, the sweet oil. There are a large number of fatty acids, but for feeding purposes 10 of them are regarded as important. In ruminant digestion, acetic acid, proprionic acid and butyric acid are very important as these are produced in the rumen and absorbed through

the wall into the bloodstream as the main source of energy for the animal. Acetic acid is known commonly as vinegar and causes the characteristic sharp taste of vinegar. Butyric acid causes the sour taste and smell. Fatty acids are important in pig nutrition and you will be seeing more of this in your lectures on pigs.


During the digestive process of the animal, lipids are broken down into glycerol and fatty acids. These are acted upon by the bile salts in the small intestine and absorbed by the villae on the walls of the small intestine, where they pass into the lymphatic system. Here they are reformed into fats, and pass into the blood stream where they are carried to the muscle and other cells where they are broken down to produce energy and heat. They are also required by the animal for the following functions:

  • They are essential for all cells and therefore must be supplied.
  • They are stored in the body as fat to act as a reserve which can be converted into energy when required.
  • Stored fat also acts as a layer of insulation for the body helping to keep out the cold.
  • Lipids act as carriers of the fat soluble vitamins around the body. They aid in the digestion of vitamin A.


The large fat (Adipose Tissue) deposits can be detected on the carcasses and they include the following:


Found just below the skin and is more noticeable in well-nourished animals. In starved animals it is absorbed, and then there is a definite outline of the spine and the animal is said to be razor-backed.


Or eye pad is a pad of fat in which the eye rests. In unthrifty animals characteristic sunken eye develops.


This is found around the udder. In males the penis runs through this fat. In castrates fat also develops in this region.


Typically noticeable in males. In females this fat can be around the uterus. If there is excess fat here, then infertility can be suspected.


This is a thick pad of fat lying between the tendinous sheets of the Abdominal Oblique Muscle.


The inner surface of the abdominal cavity or wall is lined with a thin layer of fat covered with mucous membrane.


This lines the inner surface of the thoracic cavity, can also become thick heart-fat. Anterior end deposits are throat fat. Between the two lungs, mediastinal fat occurs.



  • Brisket fat is found between the pectoral muscles and the sternum.
  • Scrotal or cod fat; when calves are castrated then the scrotum fills with lobulated fat called cod fat.
  • Hump in Zebu type cattle is muscle with fat. In the camel this is entirely fat.


  • As above, but not to the same extent.
  • The tail region in sheep tends to accumulate large deposit of fat. In fact, a bag of fat develops around the first 8 coccygeal vertebrae. In summer the deposits are particularly large; in winter these tend to be absorbed.


No major deposit in these animals, only renal fat or kidney knob resulting in a pear-shaped kidney. In sheep, this is almost spherical. Can be used to establish the difference.


Extensive in the Panniculus in the thoracic region, otherwise no other major deposits, no cod fat.


On all pigs even wild pig there are major fat deposits all over the body and this is referred to as flair.


Abdominal region only, even in starved cats.


Abdominal region
Thoracic heart region
Rump region
Abdominal region to a moderate extent


Most plants contain lipids, especially in the seeds. Of the cereals, maize has the highest content in the grain. The oil seeds of crops like cotton, soybeans and groundnuts contain very high levels of oil but this is extracted for human food, and the remainder of the seed is sold for cattle feed. Cotton cake, soybean meal and groundnut meal contain about 10% oil and are used for feeding farm animals. Soybean meal is widely used in pig feeding while the other two are used for dairy and beef cattle. Meat and bone meal contains about 10% lipids. Milk is also high in fat, which is the cream content of the milk.