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 are divided into four major groups. These are: (i) Head (ii) Thoracic cavity (iii) Abdominal cavity (iv) The limbs
(i) Head: The head is the upper part of the body. The major organs found in the head region include the brain, eyes, ears, tongue and nose.
(ii) 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.
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.
(iv) Limbs: The limbs include the forelimbs (hands) and hindlimbs (legs). They are used by farm animals for walking.
Some of the systems which maintain the body are: (i) digestive system (ii) circulatory system (iii) respiratory system (iv) nervous system (v) reproductive system (vi) Skeletal system (vii) Excretory system etc.
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 canals or digestive tracts and all the associated glands, secretory enzymes and other body fluids.
Farm animals are grouped into two main classes based on the nature of their alimentary canal or digestive tracts. 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 pigs, rabbits and poultry birds like the domestic fowls.
(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).
(a) 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.
(b) Reticulum (honeycomb): This is lined with a mucosal layer which is formed into hexagonal chamber that looks like honeycomb. It is the second compartment.
(c) Omasum (many piles): The omasum is the third and smallest compartment. It has several “leaves” or laminae/layers.
(d) Abomasum: This is the only glandular stomach. It is synonymous with the 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:
(i) Fermentation brought about by micro-organisms takes place in the rumen.
(ii) It is used for temporary storage of feed before regurgitation for proper rechewing.
(iii) Volatile fatty acids and other gases are produced in the rumen as a result of fermentation.
(iv) Absorption of volatile fatty acids takes place through the walls of the rumen.
(v) Some vitamins, e.g., vitamin B, are produced in the rumen.
(vi) Breakdown of cellulose takes place in the rumen.
Examples are the cattle, sheep and goats. They are all herbivores.
Digestion in Ruminants
Ruminant animals like cattle, sheep and goat feed mainly on grass and they can ruminate or chew the cud because of the complex nature of their stomach.
The digestion in ruminants can be explained properly with the aid of the diagram.
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 rumen, grass the is stored temporarily. In the grass is acted upon by micro organisms like bacteria and protozoa which digest the cellulose and synthesise 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
and 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 it is 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 pigs 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:
(i) 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.
ii) Stomach: In the stomach, two enzymes, enin 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 cid medium. The thick liquid called chyme now passes to the duodenum.
iii) Duodenum: Digestion also takes place here. Three enzymes are present and they act on different foodstuffs.
(a) Amylase: This enzymes converts starch to maltose
(b) Lipase: It’s converts fats and oil to fatty acids and glycerol

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