Anatomy refers to the form and structure of the body while physiology refers to the functions of the forms and parts of the body. It is very important for the farmer to understand the anatomy and physiology of farm animals because it will enable him to know more about the nutrition, reproduction and management of his animals.

The body of farm animals is divided into four major groups. These are:

  1. Head.
  2. Thoracic cavity.
  3. Abdominal cavity.
  4. The limbs.


  1. Head: The head is the upper part of the body. The major organs found in the head region include the brain, eyes, ear, tongue and nose.
  2. Thoracic Cavity: The thoracic cavity refers to the chest region of the body. The major organs in the thoracic cavity include heart, lungs and treachea.
  3. Abdominal Cavity: The abdominal cavity refers to the stomach region of the body. The major organs in the abdominal cavity: include liver, uterus, stomach, oviduct or fallopian tube, kidney, ovary, spleen, intestine, gall bladder and pancreas.
  4. Limbs: The limbs include the fore limbs (hands) and hind limbs (legs). They are used by farm animals for walking.

Some of the systems which maintain the body are:

  • digestive system.
  • circulatory system.
  • respiratory system.
  • nervous system.
  • reproductive system.



The digestive system of a farm animal includes all the organs and tissues associated with the breaking down or digestion of food in the body. It includes the teeth or beak, tongue, the alimentary canal or digestive tract and all the associated gland, secretory enzymes and other body fluids.

Farm animals are grouped into two main classes based on the nature of their alimentary canal or digestive tract. These are:

  1. Monogastric or Non-ruminant Animals: These are animals which possess only one stomach and they do not ruminate (i.e they do not chew the cud). In other words, these animals have simple stomach and cannot digest cellulose and fibres properly. Examples are the pig, rabbit and poultry birds like the domestic fowl.
  2. Polygastric or Ruminant Animals: These are farm animals which possess four stomach compartments (complex stomach) and hence, they can ruminate or chew the cud. The four stomach compartments are rumen (the largest), reticulum, omasum and abomasum (true stomach).


  1. The rumen (pounch): It has several tongue-like projections called papillae. It also has a soft towel-like appearance. It is the largest and the first compartment of the stomach.
  2. Reticulum (honeycomb): This is lined with a mucosal layer which is formed into hexagonal chamber that looks like honeycomb. It is the second compartment.
  3. Omasum (manypiles): The omasum is the third and smallest compartment. It has several “leaves” or laminae/layers.
  4. Abomasum: This is the only glandular stomach. It is synonymous with simple stomach of monogastric animals. The abomasum is the fourth and last compartment of the stomach.


Functions of the first compartment (the rumen) of the stomach of a ruminant are:

  1. Fermentation brought about by micro-organisms takes place in the rumen.
  2. It is used for temporary storage of feed before regurgitation for proper rechewing.
  3. Volatile fatty acids and other gases are produced in the rumen as a result of fermentation.
  4. Absorption of volatile fatty acids takes place through the walls of the rumen.
  5. Some vitamins, e.g. vitamin B, are produced in the rumen.
  6. Breakdown of cellulose takes place in the rumen.

Examples are the cattle, sheep and goat. They are all herbivores.


Digestion in Ruminants

Ruminant animals like cattle, sheep and goat feed mainly on grasses and they can ruminate or chew the cud because of the complex nature of their stomach.

When a ruminant animal like a cow wants to feed, it cuts the grass and swallows it with minimal chewing. The grass passes from the mouth through the oesophagus to the rumen where the grass is stored. In the rumen, the grass is acted upon by microorganisms like bacteria and protozoa which digest the cellulose and synthesize some amino acids needed by the animal from non-protein nitrogenous substances.

When the cow has finished filling the rumen, it finds a cool place and lies down quietly. By anti-peristaltic movement of the stomach, the undigested grass passes from the rumen to the reticulum from where it re-enters the oesophagus (regurgitate) back to the mouth. The food is now chewed properly by using the molar and premolar teeth (chewing the cud) into a semi-liquid cud which is re-swallowed. This liquid cud now moves into the omasum from where it passes to the abomasum (the true stomach). The whole process is called. rumination.

In the abomasum, enzymes are secreted which act on the food. Further digestion and absorption of the food take place progressively along the digestive tract. The digested food is then absorbed into the blood through the villi in the small intestine while the undigested food passes to the large intestine where they are removed through the anus as dung or faeces.


Digestion in Non-ruminant (Pig)

Pig has only one stomach. It does not chew the cud neither does it utilise roughages

properly. The digestion in pig can be understood properly with the aid of the diagram.

The pig feeds mainly on basal feeds like maize, cassava and other mashed food. Digestion of food takes place in four areas of the tract:

  1. Mouth: In the mouth, the food is chewed and mixed with saliva which contains an enzyme called ptyalin. The ptyalin converts starch to maltose. The food is now swallowed and moves by peristaltic movement to the stomach.
  2. Stomach: In the stomach, two enzymes, renin and pepsin, are present. Renin acts on milk or it helps to curdle milk while pepsin converts proteins to peptones under the influence of an acid medium. The thick liquid called chyme now passes to the duodenum.
  3. Duodenum: Digestion also takes place here. Three enzymes are present and they act on different food stuffs:
  • Amylase: this enzyme converts starch to maltose.
  • Lipase: converts fats and oil to fatty acids and glycerol.
  • Trypsinogen: converts protein and peptones to polypeptides. These enzymes are secreted by the pancreas. The digestion of fats and oil is aided by bile which is secreted by the liver and stored in the gall bladder. The bile helps in the emulsification of fats. At the end of digestion in the duodenum, the food (now in liquid form) called chyle passes to the ileum or small intestine.

4. Small Intestine: The wall of the small intestine secretes many enzymes which complete the process of digestion.

The enzymes are:

  • Lipase which converts fats and oil to fatty acids and glycerol.
  • Erepsin converts polypeptides to amino acids.
  • Maltase converts maltose to glucose.
  • Sucrase converts sucrose to glucose and fructose.
  • Lactase converts lactose to glucose and galactose.

The end product in the digestion include the conversion of:

  • protein to amino acids.
  • starch to glucose.
  • fats and oil to fatty acid and glycerol.

These end products (amino acids, glucose and fatty acid and glycerol) are absorbed in the small intestine by a structure called the villi. The undigested food materials are passed to the large intestine from where they are ejected through the anus as faeces or dung.

The digestion of food in rabbit (a non-ruminant) is just like the pig except that rabbit can feed properly on grasses which are digested in the large caecum which contains micro-organisms like bacteria and protozoa.


Digestion in Domestic Fowl

The domestic fowl is a monogastric animal and has a simple stomach. Digestion in fowl can be explained properly with the help of the diagram.

The fowl has no teeth but the food is picked up by the beak. This food then passes on to the crop through the oesophagus. This food is stored temporarily in the crop where it is moistened and fermented by some bacteria. The food now passes on to the proventriculus where digestive enzymes are secreted on the food.

The proventriculus is often regarded as the glandular stomach because it secretes digestive enzymes on the food like pepsin and amylase.

From the proventriculus, the food moves to the gizzard where grinding takes place. With the aid of small stones or grits, the food is ground by the gizzard. From the gizzard, the food now moves to the duodenum and small intestine where further digestion and absorption take place while the undigested food materials are removed from the tract as faeces.


Differences Between Monogastric and Ruminant Animal Digestive System

Monogastric Animal

  1. Possesses only one.
  2. It cannot ruminate or chew the cud.
  3. It cannot digest cellulose and fibres properly.
  4. Digestion is not aided by bacteria.
  5. Its diet is mainly basal and concentrate feeds.
  6. It cannot synthesize its own proteins unless supplied in the feed.
  7. It does not regurgitate.
  8. It has no rumen.
  9. Poultry, rabbits and pigs are examples.


Ruminant Animals

  1. Possesses four stomach compartments.
  2. It can ruminate and chew the cud.
  3. It can digest cellulose and fibres very well.
  4. Digestion is aided by bacteria.
  5. Its diet is mainly grasses and other cellulose e.g. legumes.
  6. It can synthesize its own protein through microbial activities in the rumen.
  7. It regurgitates.
  8. It has rumen.
  9. Cattle, sheep and goats are examples.


Importance of Digestive System

  1. It aids the ingestion of feed.
  2. It promotes the digestion of feed.
  3. It ensures the absorption of digested feed.
  4. It helps in ejection of undigested feed.
  5. It aids the secretion of productive hormones and digestive enzymes.

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