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SUB TOPIC 3: Digestive system, Circulatory system and Respiratory system
A: DIGESTIVE SYSTEM: Digestion is the process by which insoluble food substances are broken down into simple soluble and absorbable compounds. It occurs in alimentary canal such as the mouth, oesophagus, stomach, small intestine, large intestine and accessory glands such as salivary gland, the liver and the pancreas. The functions of digestive system are ingestion, grinding, digestion, absorption of digested food and elimination of solid waste. Based on alimentary canal, farm animals can be grouped into monogastrics (non ruminants) and polygastrics (ruminants).
DIGESTION IN RUMINANTS
Ruminants are animals that have complex stomachs and equally chew the cud. The stomach is:
- Rumen
- Reticulum
- Omasum
- Abomasum
They feed on grasses and chew a little bit, thereafter the grasses pass to the rumen where microorganisms act on them and digest it to form amino acids. When rumen is filled, the animal at a quite time regurgitate the grasses through antiperistaltic movement for a proper chewing. The food then passes to the reticulum and omasum for further breakdown of cellulose and goes into abomasums for secretion of enzymes. The food finally goes to duodenum (small intestine) for the absorption of nutrients. This completes the digestion process. The undigested and unabsorbed materials are removed through the anus as waste.
DIGESTION IN MONOGASTRICS
Non-ruminants are animals with only one stomach and they do no chew the cud e.g pig, poultry, rabbit, horse etc. They feed mostly on concentrates. The feed gets to the stomach after chewing with a mixture of saliva. Enzymes acts on the feed in the mouth which converts them to other end products. The product moves to the duodenum and small intestine. The process is completed in the small intestine with enzymes such as lipase (noted to convert fat and oil to fatty acids), trypsin (which convert polypeptide to amino acids), maltase (which convert maltose to glucose), sucrase (converts sucrose to glucose and fructose) and lactase (converts lactose to glucose and galactose)
At the end of digestion process, protein is converted to amino acids, starch to glucose and fats and oils to fatthy acids which are all absorbed in the small intestine through the villi. However, the undigested food materials move to the large intestine and is eventually excreted through the anus of the animals as faeces.
DIGESTION IN BIRDS
The fowl has a simple stomach but makes use of beak to feel and pick the feed. The feed follows this movement pattern: from oesophagus to the crop (where fermentation takes place) to the proventriculus (where digestive enzymes pepsin, HCL and amylase act on the food) to the gizzard (grinding of food by grits takes place here) and finally to the duodenum and small intestine (where digestion and absorption of food take place).
DIFFERENCES BETWEEN MONOGASTRIC AND POLYGASTRIC DIGESTION
| Monogastric | Polygastric |
| One stomach chamber | Four stomach chamber |
| They cannot chew cud | They can chew cud |
| They cannot digest cellulose properly | They can digest cellulose properly |
| Digestion is not aided by bacteria | Digestion is aided by bacteria |
| They cannot synthesize amino acids unless supplied | They can synthesize their own amino acids via microbial activity |
| They cannot regurgitate | They can regurgitate |
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