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:
Mono gastric 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.
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, omasun and abomasun (true stomach).
The rumen (pouch): It has several tongue-like protections called papillac. It also has a soft towel-like appearance. It is the largest and the first compartment of the stomach.
Reticulum (hone comb): This is lined with a mucosal layer which is formed into hexagonal chamber that looks like honeycomb. It is the second compartment.
Omasun (manypiles) The omasun is the third and smallest compartment. It has several “leaves” or laminae/layers.
Abomasun: This is the only glandular stomach. It is synonymous with simple stomach of monogastric animals. The abomasun 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 re-chewing
(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
(vii) 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 it stored. In the rumen, the grass is acted upon by micro-organisms 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 omasun from where it passes to the abomasun (the true stomach). The whole process is called rumination.
In the abomasun, 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 utilize roughages properly. The digestion in pig can be understood properly.
The pig feeds mainly on basal feeds like maize, cassava and other mashed food. Digestion of food takes place in four area 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, rennin and pepsin, are present. Rennin 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 chime now passes to the duodenum.
(iii) Duodenum: Digestion also takes place here. Three enzymes are present and they act on different food stuffs
(a) Amylase: this enzyme converts starch to maltose
(b) Lipase: converts fats and oil to fatty acids and glycerol
(c) Typsinogen: 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 emulificaton of fats. At the end of the digestion in the duodenum, the food (now in liquid form) called chyle passes to the ileum or small intestine.
(iv) Small intestine: The wall of the small intestine secretes many enzymes which complete the process of digestion.
The enzymes are:
(a) Lipase: which converts fats and oil to fatty acids and glycerol
(b) Erepsin converts polypeptides to amino acids
(c) Maltose converts sucrose to glucose.
(d) Sucrose converts sucrose to glucose and fructose
(e) Lactose converts to glucose and galactose.
The end product in the digestion include the conversion of:
(i) Protein to amino
(ii) Starch to glucose
(iii) Fats and oil in amino acids
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 mirco-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.
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 preventriculus is often regarded as the glandular stomach because it secretes digestive enzymes on the food like pepsin and amylase.
From the preventriculus, 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.
IMPORTANCE OF DIGESTIVE SYSTEM
(i) It aids the ingestion of feed
(ii) It promotes the digestion of feed
(iii) It ensures the absorption of digested feed
(iv) It helps in ejection of undigested feed
(v) It aids the secretion of productive hormones and digestive enzymes
HERE YOU WILL FIND EVERY AVAILABLE TOPICS ABOUT AGRICULTURAL SCIENCE AND BIOLOGY. AND THE LINKS TO THEIR VARIOUS SOURCES.
1. DEVELOPMENT OF AGRICULTURE
2. IMPORTANCE OF AGRICULTURE
3. SUBSISTENCE AGRICULTURE
4. COMMERCIAL AGRICULTURE
5. PROBLEM OF AGRICULTURAL DEVELOPMENT
6. SOLUTIONS TO POOR AGRICULTURAL DEVELOPMENT
7. AGRICULTURAL LAWS AND REFORMS
8. ROLES OF GOVERNMENT IN AGRICULTURAL DEVELOPMENT
9. AGRICULTURAL POLICIES
10. PROGRAM PLANNING IN AGRICULTURE