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Reg. No.: 2011/011959/07
Agricultural Sciences
Study guide
Grade 12
CAPS aligned
JC Zandberg
LESSON ELEMENTS
LEARNING AIMS
What the learner should know at the end of the lesson. Taken from CAPS.
IMPORTANT TERMINOLOGY
New terminology to extend understanding of the subject as part of the lesson.
DEFINE
Definitions of concepts to help the learner understand the content.
IMPORTANT
A summary or explanation of key concepts explained in the lesson.
TIPS
Sample
Information in addition to the content to guide the learner through the learning process.
FOR THE CURIOUS
Encouragement for the learner to do in-depth research about the content on his/her own.
ACTIVITY
Formative assessment to test the learner’s progress and knowledge of the lesson completed.
EXERCISE
Formative assessment to test the learner’s progress and knowledge of the unit completed.
CORE CONTENT
Sample
Reinforcement of core of content; in-depth explanation of a specific section of the lesson.
STUDY / REVISION
Demarcation or summary of work to be revised in preparation for tests and examinations.
PREFACE
ADDITIONAL SOURCES
Study and Master CAPS, Altys Strydom, Henricho Ferreira, Peter J Holmes
Agricultural Sciences for All by W Burger, N Phewa, M Burger
Focus on Agricultural Sciences by J de Fontaine, B Letty, K Morrison, A Smuts
Magazines such as Farmer’s Weekly; Agri Farmer, The Dairy Mail, Stock Farm, Red Meat.
What does Agricultural Sciences involve?
Agricultural Sciences is the study of the relationship between ground, plants and animals in the production and processing of food, fibre, fuel and any other agricultural product that has an economic, aesthetic and cultural value. It is an integrated science that combines knowledge and skills of Physical Sciences, Life Sciences, Social Sciences, Geography, Engineering, Mathematics and Economics.
This subject must be seen within the holistic science framework and not as an isolated science. With this subject, Agricultural Sciences, a sustainable agricultural environment is embedded by integrating theory and skills in the study of the food production chain and processing. It focuses on the management skills needed to sustain production in a viable way.
UNIT 1: Animal nutrition and digestion
Lesson 1: Animal nutrition
LEARNING AIMS
You will be introduced to:
• The external structure of the alimentary canal of a ruminant (cow and sheep) and non-ruminant (fowl and pig).
• Functions and adaptions of various structures of the alimentary canal.
• The internal structures of the following:
• Rumen
• Reticulum
• Omasum
• Abomasum
• Small intestine
An animal can be compared to a car. Like a car, the animal can move around and needs fuel to do so. In the car’s engine, fuel is consumed by internal combustion for the production of mechanical energy. Oxygen is needed for the internal combustion of fuel. Waste products (fumes) are generated and removed through the exhaust. In animals, food serves as fuel, and is broken down through the process of respiration, releasing energy. For respiration, oxygen is inhaled, while the waste products (carbon dioxide and water) are exhaled
IMPORTANT TERMINOLOGY
• Ruminant: Animals with a stomach that consists of four compartments. They swallow their food without chewing it and later it is regurgitated and rechewed before it is re-swallowed to be digested.
• Non-ruminants: Animals with a single-chambered stomachs and they are monogastric.
• Cud: Partly digested food that is returned from the stomach to be rechewed.
• Fermentation: The process whereby microorganisms break down fibres.
• Enzymes: is pH-specific.
• Saliva: A thin, colourless, watery and somewhat sticky alkaline fluid.
• Ingestion: The intake of large food molecules into the mouth where digestion starts.
• Digestion: Physical and chemical processes take place with food to put it into simpler, soluble substances.
• Absorption: The end products of digestion are transported through the wall of the rumen into the bloodstream and lymphatic system to be distributed to all the cells in the body.
• Transportation: The nutrients that are absorbed, are transported to various cells in the body for energy, building material and/or repairing material.
• Assimilation: When the ingested food is taken up by the cells of the body.
• Egestion: When the indigestible waste products are eliminated from the body.
• Chyme: Thick liquid remaining after chemical digestion.
• Secretion: Digestive juices are secreted by different organs in the digestive tract to break down food into smaller particles. These secretions include saliva, gastric juices, pancreatic juice, bile and intestinal juice.
Sample
The essential function of the animal in a solid agro-ecosystem is the conversion of a large part of the agricultural products that are unfit for human consumption, such as roughage, in other more suitable forms such as meat and milk, which can be used by man.
Animal nutrition affects the farmer directly and indirectly. Indirectly because its task is to produce food for humans and directly as an essential part of that responsibility involves the economic conversion of plant to animal products.
Feed costs are the single largest expense in the production costs of livestock production. The rights and scientific nutrition of farm animals will largely determine whether there will be farmed profitably. Therefore, a thorough knowledge of animal nutrition is a prerequisite for successful livestock farming.
Animal food varies and can contain many useless material. Because of this difference in nutritional requirements and food sources we distinguish between:
• Herbivores (plant eaters), for example sheep, cattle and goats.
• Carnivores, animals that feed on herbivores e.g. lions and eagles
• Omnivores eat plants and animals such as monkeys, baboons and pigs
To solve this problem, the animal owns its own built-in refinery, the digestive system, which extracts the useful ingredients from the food and is the digestive systems of the different kinds of animals adapted to meet their nutritional requirements.
The digestive system consists of the digestive tract and related organs. The digestive tract of the animal consists of the following parts:
• Mouth
• Pharynx
• Esophagus
• Stomach
• Small intestine
• Colon (large intestine)
• Rectum
• Anus/cloaca
A comparison on the external structure of the alimentary canal of a ruminant and non-ruminant
There are many adjustments made by herbivores, carnivores and omnivores according to their specific nutritional requirements and diets. Farm animals are divided into two groups namely:
RUMINANTS
Sample
Cattle Sheep
Ruminants are mostly herbivores such as cattle, sheep and goats. Herbivores have competition when it comes to the search of food, so they have developed very different ways of eating. Cattle and sheep eat mainly grass and small plants and are capable of utilising indigestible roughage and low quality feed which consists mainly of cellulose. Ruminants that are also herbivores eat large amounts of plant material to meet their energy needs and have more than one stomach to digest cellulose.
NON-RUMINANTS
Chickens Pigs
Non-ruminants are monogastric, thus they have a single-chambered stomach. The digestive system of the non-ruminants is very simple. They eat the least amount of food because their diet is rich in all the nutrients they need, as well as proteins.
The differences between ruminants and non-ruminants:
• Complex stomach consisting of the rumen, reticulum, omasum and abomasum.
• Food is swallowed and regurgitated for re-chewing and re-swallowing.
• They can digest fibrous plant material (cellulose).
• Ruminants are herbivores.
• Monogastric stomach consisting of only one compartment.
• Food is chewed and swallowed only once.
• They cannot digest fibrous plant material.
• Non-ruminants may be omnivores or herbivores.
The digestive system/alimentary canal/gut consists of organs for:
- ingestion or intake of food (mouth, pharynx and oesophagus)
- The digestion and absorption of food (stomach, small intestine and large intestine)
- and the excretion/egestion of waste products (rectum/anus)
Supplementary digestive organs include lips, teeth, tongue, salivary glands, liver and pancreas.
Digestion in non-ruminants
Large intestine: Consists of the caecum and proximal colon
Endocrine gland: A gland that secretes hormones directly into the bloodstream.
A hormone: It is a substance secreted into the blood that acts on tissues in other parts of the body and then produces a biological response.
Exocrine gland: A gland that secretes its products into ducts.
Gluconeogenesis: A metabolic process in which glucose is synthesised.
Non-ruminants have monogastric digestion because the stomach consists of only one compartment.
• Digestion is the breakdown of large particles into smaller particles of food that can be absorbed by the cells in the body.
• Mechanical digestion involves chewing/mastication and grinding with the teeth as well as the churning actions of the stomach that turn feed into pulp.
• Chemical digestion involves digestive enzymes that break down large molecules of carbohydrates, fats and proteins into simpler substances.
CORE CONTENT Sample
• Study the digestive systems of ruminants and non-ruminant that follows.
• Compare various components the digestive tracts of ruminants and nonruminants in a table as shown below.
• It is important to make sure that you know all the names and understand them.
Draw the following table and complete it as you work through the lesson content. Complete it as fully as possible. It will serve as a summary to help you with revision.
RUMINANTS NON-RUMINANTS CATTLE PIG
Mouth
Salivary gland
Teeth
Stomach
Small intestine
Liver
Large intestine
Anus/cloaca
An animal’s food is physically and chemically simplified in the digestive system before it is digested and used by the body. The digestive system consists of a long, tubular organ, with various enlargements, folds, twists, as well as the digestive glands that end in the canal and secretes digestive juices There are length and circular muscles in the walls of the alimentary canal that help with the movement of food through the channel.
THE INTAKE OF FOOD
LIPS
Food is taken in through the mouth. Because the thick, virtually immovable lips of cattle are relatively insensitive, foreign objects such as pieces of wire and nails are often swallowed.
FUNCTIONS OF THE LIPS
• They close the mouth cavity and prevent food from falling out of the mouth.
• When cattle drink water, the lips lock tightly, except for a small opening through which the animal can suck the water in. When the calf suckles on the cow, the lips lock tightly around the teat and the milk is sucked out.
TONGUE
The tongue is a muscular organ that is particularly movable and contains many taste buds. After cattle have picked the plant material off with a jerking movement, it is rolled into a cylindrical shape with the tongue and swallowed virtually whole. The papillae on the tongue help to keep food together.
A rare, hereditary phenomenon in some cattle is the presence of a smooth tongue. It is usually caused by the absence of papilla, and these cattle can consequently not graze properly and become emaciated.
FUNCTIONS OF THE TONGUE
• It mixes food thoroughly with saliva.
• It helps to keep food between the teeth.
• It helps to swallow food.
• The taste buds on the tongue enable the animal to distinguish between tasty and less tasty food. It explains why animals graze selectively.
• The tongue helps to feel strange objects in the food.
• In the case of cattle, the tongue is used to pick grass with a jerking motion.
TEETH
The finer an animal chews its food, the easier and better digestive juices can affect it. This is why animals should have enough time to graze and why food must often be treated beforehand.
TYPES OF TEETH AND THEIR FUNCTIONS
• The eight chisel-shaped incisor teeth are all found in the lower jaw and are used to “cut off” the grass.
• Cattle have no canine teeth.
• The 12 premolars and the 12 true molars are spread evenly between the upper and lower jaws. They grind the food during the rumination process.
FOR THE CURIOUS Sample
The swallowing process is a complex reflex action that involves 25 different muscles. Ruminants produce large quantities of saliva per day. The saliva of ruminants does not contain the enzyme amylase and therefore no chemical digestion takes place in the mouth.
Glands in the mouth that secretes saliva:
• Parotid glands produce a watery serous secretion.
• Submaxillary glands produce a mixed serous and mucous secretion.
• Sublingual glands secrete saliva that is predominantly mucous in character.
FUNCTIONS OF SALIVA IN THE RETICULORUMEN
• It maintains the pH of the rumen.
• It provides fluid for fermentation.
• It is involved with recycling nitrogen to the rumen.
• Saliva acts as an alkaline buffer that neutralises the acid produced in the rumen and the reticulum during fermentation.
DIGESTION IN THE STOMACH OF THE RUMINANT
The stomach of the ruminant consists of four compartments: rumen, reticulum, omasum and abomasum, each with a specific number of functions. The first three compartments or chambers, the rumen, reticulum and omasum, are known as the fore stomach. The rumen and reticulum also function as one organ, called the reticulum-rumen and contains approximately 84% of the total stomach.
DESCRIPTION
RUMEN (Paunch)
The rumen is the first compartment and also the biggest of the four stomach compartments of ruminants and makes up 80% of the total stomach volume of the adult ruminant. It consists of a dorsal and ventral bag. The content capacity varies depending on the size and age of the animal. It is usually in the region of 4 to 10 litres in sheep, 3 to 6 litres in goats and 100 to 300 litres in cattle.
The rumen is lined with epithelial that resemble a thickly sticky mass of papilla that look like protrusions, which increases the absorption level of the rumen and functions as heating bars.
Internal structure of the rumen (1), reticulum (2), omasum (3) and abomasum (4) of goats.
Photo courtesy of G. F. W. Haenlein, University of Delaware.
In the reticulorumen, which can be seen as a large fermentation barrel, the animal secretes no digestive juices or enzymes. However, food undergoes a rather wide variety of digestive and synthetic processes. These digestive and synthetic processes are performed by microbes that live inside the organ in a symbiotic relationship with the host.
FUNCTIONS OF THE RUMEN
• The rumen contains of many microorganisms, such as bacteria and protozoa, which breaks down cellulose and lignin found in plant material.
• Microbiological activity in the rumen leads to the successful conversion of starch and fibre of feeds, to important volatile fatty acids such as acetic acid, propionic acid and butyric acid.
• Microbiological digestion in the rumen is the reason why ruminants can utilise fibrous feeds effectively as food.
• These volatile fatty acids are absorbed through the rumen wall and provide as much as 80% of the animal’s total energy requirements.
• The rumen provides the correct pH for the functioning of microorganisms that are needed for the digestion of cellulose in plant material.
• Rumen microbes also break down components of food into useful products such as essential amino acids, B-complex vitamins and vitamin K.
• Rumen microorganisms produce large quantities of gases, mainly methane and carbon dioxide.
• Contractions of the rumen and reticulum help with the flow of finer food into the omasum.
RETICULUM (Honeycomb stomach)
No digestive juices are discharged here The reticulum wall looks just like a honeycomb. Food is mixed by means of contractions. From the oesophagus, there is a gutter-shaped swallowing groove through the rumen and reticulum right up into the abomasum. This compartment is sometimes called the “hardware stomach” as this is where hard objects such as nails, wire and foreign objects ingested with the food settle.
FUNCTIONS OF THE RETICULUM
• Acts as a filter that allows small digestible food particles and fluids to pass through to the omasum and abomasum.
• Helps with the absorption of volatile fatty acids.
• Traps hard indigestible substances such as wires that are ingested accidentally.
• Boluses for regurgitation and rumination are formed in the reticulum.
OMASUM (Manyplies)
The omasum has many foliated protrusions that prevent rough food from moving further to the abomasum. There are four types of folds:
• Primary folds (largest)
• Secondary folds (smaller)
• Tertiary folds (even smaller)
• Quaternary folds (smallest)
These folds press the remaining rough food particles together and grind and grate them between the powerful hornlike muscular folds. The food is dried out here.
FUNCTIONS OF THE OMASUM
• It helps with the absorption of some volatile fatty acids.
• 60 – 70% of water is absorbed in the omasum.
• Papillae are used to grind food.
• It acts as a temporary storage site.
• Fluids and finally digested feed particles are filtered before passing through to the abomasum.
• Large substances are sent back to the rumen and reticulum.
• Feed particles are further broken down into smaller molecules.
ABOMASUM (True stomach – glandular stomach)
• The abomasum functions like the single-chambered stomach of a monogastric animal.
• The abomasum can be compared with the singular stomach of non-ruminants.
• The pylorus sphincter is located in front, where it is connected to the duodenum.
• The abomasum is lined with epithelial tissue.
• Gastric juices are secreted here, therefore enzymatic digestion starts in the abomasum.
• The secretion of hydrochloric acid makes the abomasum very acidic.
FUNCTIONS OF THE ABOMASUM
• Two enzymes are secreted here: Rennin curdles milk. Pepsin digests and break down proteins.
• Chyme is sent to the small intestine.
• The muscular walls of the abomasum churn the food.
• Digestive enzymes, gastric juices and hydrochloric acid are secreted by cells in the abomasum. It helps proteins in food and microbes that are mixed with food, to hydrolise.
