farm animal biological systems - .global - digestion in non-ruminants.pdf · farm animal biological...

www.lbcnc.org.uk

Farm animal biological systems

Pack 5

Digestion in non-ruminants Pack Code: ABS05

This pack you will help you to:

• explain the function of the major

types of digestive system.

• list the main parts of the major types

of digestive system.

• understand the differences between

ruminant and non ruminant digestive

systems.

Farm animal biological systems 2

About this pack

Objectives

When you have completed this pack you should be familiar with the

function and main features of the major types of digestive system.

The pack will help you to:

• explain the function of the major types of digestive system

• list the main parts of the major types of digestive system

• understand the differences between ruminant and non ruminant digestive

systems.

The pack is also relevant to the level 3 unit Understand Animal Anatomy

and Physiology, and in particular to:

• Outcome 1: Know the structure and functions of biological systems in

animals

• Outcome 4: Understand how an animal’s body structure and systems are

adapted to its environment.

It is also relevant to the level 3 unit Understand the Principles of Animal

Nutrition, and in particular to: Outcome 1: Understand the functions of the

main components of an animal’s diet

Links to other packs

This is one of a series of learning packs, each tackling an aspect of farm

animal biology. They are:

• ABS1: The skeleton

• ABS2: Joints

• ABS3: Circulation

• ABS4: Respiration

• ABS5: Digestion in non-ruminants

• ABS6: Digestion in non-ruminants

• ABS7: Digestion in horses

• ABS8: The reproductive system

• ABS9: Oestrus and hormones

• ABS10: Gestation and birth

• ABS11: How animal cells work

• ABS12: How animal cells divide

• ABS13: Connective and epithelial

tissue

• ABS14: Muscle and nervous tissue

• ABS15: Sensory organs

• ABS16: Introduction to genetics

• ABS17: Meiosis

• ABS18: Inheritance

• ABS19: Selective breeding

• ABS20: Breeding technology

• ABS21: The lymphatic system

• ABS22: The endocrine system

• ABS23: The nervous system


Overview of the digestive system

Food contains both useful elements such as carbohydrates, proteins, oils (fats

if animal in origin), minerals and vitamins and waste elements which the

body is unable to digest and use. The digestive system separates the useful

components from the waste.

The purpose of the digestive system is to:

• mechanically and chemically digest food – breaking down complex food

substances into simpler substances

• allow the absorption of food – through the wall of the digestive tract and

into the blood

• assimilation – using the simple products of digestion for maintaining the

body, growth, milk production and pregnancy.

• assist the elimination of solid waste :

– Substances that are not used by the body after they have been

absorbed will be removed by excretion through perspiration and

urination.

– Substances that are not digested are removed by egestion, for

example, dung.

The digestive system has muscles running along its entire length. These help

to move and churn up the food. Digestion is also helped by other organs,

such as the liver, that produce chemicals to break down the food.

The digestive tract

The digestive tract is a continuous tube running from the mouth to the anus.

This is where the process of digestion takes place. The main parts of the

digestive tract are the:

• mouth or ‘buccal cavity’

• oesophagus

• stomach

• small intestine – linked to the:

gall bladder

liver

pancreas

• large intestine – including colon, caecum and rectum

• anus.


Two types of digestive system

There are two types of digestive system, ruminant and non-ruminant. The

differences between them are mainly in the stomach:

• ruminants have a complex system of four stomachs that are capable of

digesting complex roughage (plant material) into starches and sugars

which can then be used by the animal. Cows and sheep are ruminants

• non-ruminants have a more simple system such as that found in pigs (and

humans) where only one stomach is present.

Review quiz 1

Which of these diagrams shows a simple or non-ruminant and which

shows a complex or ruminant digestive system?

Picture 1

Picture 2

The answer is at the end of this pack. This pack looks at the simple stomach.


The function of the mouth and teeth

Food digestion starts with the mouth. The mouth grasps, grinds and chews

food. This is an important part of mechanical digestion.

Prehension

Gathering food ready to be put into the mouth is termed prehension.

Humans have hands which we use to gather food; they are our organs of

prehension. Farm animals do not have hands, and can be divided into three

groups

1 The graspers

2 The nibblers

3 The gobblers

A cow is a grasper. Next time you are in a field with cows watch them graze.

The tongue is covered in many papillae (projections) which give it a rough

feel. It comes out, grasps the grass and pulls it back over the incisor teeth

into the mouth. Because they use a pulling action, cattle can do a lot of

damage to a new ley. As the roots are young and shallow, anchoring is poor

and the plants can easily be pulled out of the ground.

Sheep are nibblers using the incisors and the dental pad. This gives a much

gentler action on the pasture. The grass is nibbled off very close to the

ground. This is a milder action then the grasping of cattle and encourages

tillering of the sward, ideal for a new ley.

Pigs are gobblers. Their shovel like lower jaw is designed to root and scoop.

They can cause tremendous damage to pastures unless they are ringed.

Teeth

The teeth are the hardest structures in the animal body. They cut, shear and

grind the food.

There are four types of teeth:

• Incisors or broad teeth (the front teeth) used for nibbling and shearing,

found in all animals

• Canine, dog or eye teeth used for tearing, found in humans, pigs, dogs etc,

but not found in ruminants

• Premolars used for grinding, found in all animals

• Molars used for grinding, found in all animals.


Activity

Why does the animal need to grind up its food?

The answer is at the end of this pack.

Chewing

Chewing is the mechanical breakdown of food using the teeth, tongue and

cheek muscles. Chewing reduces the physical size of the food making it

easier to swallow and easier to chemically digest in the digestive tract.

Why does chewing speed digestion? Chewing breaks the food down into

smaller chunks, and in doing so increases the surface area of the food.


Activity

Measure the total distance around the bottom four lumps and compare it

to the distance around the top lump.

Check your answer with the one at the end of this pack

Imagine the top lump is a piece of food before chewing and the bottom

four is the food after chewing. Although the total amount of food is the

same, the chewed food has double the surface area. An increased surface

area gives a bigger surface for digestive chemicals or bacteria to act on and

so increases the speed of digestion

Saliva

Saliva produced in the mouth is the first of the digestive juices. Saliva is a

fluid produced by salivary glands in the mouth. Its functions are to:

• to lubricate the food, and make it easier to swallow

• to dissolve chemicals in the food to stimulate the taste buds.

Swallowing

Swallowing involves the tongue moving up and back, pushing the food into the pharynx (throat) where

muscles contract pushing the food into the oesophagus.

The oesophagus is a muscular tube leading from the throat to the stomach.

Once food enters the oesophagus the muscles contract (peristalsis) forcing

the food along into the stomach.


Review quiz 2

1 Which of the following would be best suited to grazing a new

grass ley:

! a) cows

! b) pigs

! c) sheep

2 Which of the teeth listed below are used for grinding the food?

! a) canine

! b) molars

! c) incisors

The simple stomach

Structure of the stomach

The simple stomach is present in monogastric animals such as pigs and

humans. The last part of the ruminant stomach (the abomasum) is also very

similar to the simple stomach.

The stomach is a bag which lies between the oesophagus and the small

intestine. It is used to store, digest and acidify food. Part of the stomach is

glandular, which means that it has structures (glands) which produce and

secrete digestive juices. This is where chemical digestion starts. Food

entering the stomach is gradually mixed with the food already present and

the gastric juices. The stomach walls are protected from the digestive

enzymes by a thick layer of mucus.

Gastric juice

Gastric juice contains hydrochloric acid, pepsin and bacteria. The gastric

juice of young animals also contains rennin, which helps digest milk. All of

these play an important part in digestion, and their function is explained

below.


Hydrochloric acid

The action of hydrochloric acid gradually reduces the pH of the food to

around pH 2. This is not instantaneous and can take from two to twelve

hours after feeding.

One of the functions of the acid is to kill bacteria which are taken in with the

food. Since it takes several hours for all the food to become acidic it is

possible for bacteria to enter the small intestine and cause disease. This is one

reason why good feeding management is so vital.

Pepsin

This is an enzyme which starts off the digestion of protein into smaller

chains called peptides. Pepsin is produced in an inactive form called

pepsinogen and changed to pepsin by the action of hydrochloric acid.

Enzymes are produced by glands, and sometimes need to be released in an

inactive form to prevent the glands from self-digesting.

Bacteria

There are bacteria in the stomach, as in the rest of the gut. The bacteria

(lactobacilli) ferment food, producing organic acids such as Lactic acid.

These bacteria are essential to the well being of the gut.

Rennin

Rennin is found in the stomachs of young animals. It coagulates milk into

curds (solids) and whey (liquid). Coagulation of milk reduces the speed at

which it leaves the stomach and this allows hydrochloric acid and pepsin to

have their full effect. The whey leaves the stomach very quickly, but the curd

is gradually digested by the pepsin.

Leaving the stomach

When the food has been digested and the top part of the small intestine

(called the duodenum) is empty, a valve at the bottom of the stomach called

the pyloric sphincter opens. The food, now called ëchymeí, is forced out of

the stomach through this valve and enters the small intestine.


Large intestine

Review quiz 3

1 Hydrochloric acid acts to:

! a) reduce the pH of food

! b) increase the pH of food

! c) allow bacteria to breed

2 Rennin is found in the gastric juice of all animals

! True ! False

3 After the food leaves the stomach it enters:

! a) the large intestine

! b) the small intestine

! c) the oesophagus

The intestines

The intestines are long tubes running from the stomach to the anus. They are

divided into two parts:

• the first part is the small intestine is thin but very long – in the pig it is

about 18 metres! The primary function of the small intestine is to absorb

useful materials from food.

• the second part is the large intestine is wider but shorter. The primary

function of the large intestine is to absorb water and so prevent it being

lost from the body in the faeces.

Rectum

Stomach Oesophagus

Caecum

Colon

Pyloric sphincter

Duodenum Jejunom Ileum

Small intestine


The small intestine

The small intestine is made up of the duodenum, the jejunum and the ileum.

In the duodenum Brunner’s glands secrete alkaline fluid, neutralizing the

acid from the stomach to about pH 7-8, at which level digestive enzymes can

function properly. The duodenum also connects to three organs which

secrete chemicals needed for digestion:

• The liver produces bile and the gall bladder concentrates and releases

this. Bile emulsifies fats, turning them into many smaller droplets. This

increases the surface area for the fat digesting enzyme, lipase, to act on.

• The pancreas produces specialized enzymes including lipase to digest fats

and tripsin to digest proteins. These break the food down into parts small

enough to be absorbed through the intestine walls.

Food passes through the jejunum into the next section of the small intestine,

the ileum. This is where most absorption occurs, as sugars, amino acids,

vitamins and minerals are absorbed into the bloodstream.

This cross section shows how a series of layers of tissue in the ileum

surround the lumen – the space through which food passes.

• The ileum is lined with mucosa. This has many small projections – villi –

which increase the surface area for absorbing nutrients. They also contain

lacteals – lymphatic capillaries that help absorb fatty acids and glycerols.

• Nutrients pass through the mucosa to the submucosa, where they are

absorbed into blood vessels and can pass into the blood. The submucosa

also contains nerves which help coordinate digestion.

• After this there are layers of muscle tissue, Waves of muscle contraction

move food down the intestine. This action is known as peristalsis.

• Finally a further layer of tissue is called the serosa.

High oil diets can produce soft body fat. This is why oily feed should be

restricted in the final ration of meat producing animals.

Submucosa with nerves and blood vessels

The lumen

Circular muscle layer

Longitudinal muscle layer Serosa

Muscle contraction keeps food moving

Mucosa with villi and lacteals


Review quiz 4

1 Bile is secreted from:

! a) the stomach

! b) the gall bladder

! c) the pancreas

2 The function of bile is to:

! a) digest fats

! b) neutralise acid

! c) emulsify fats

3 Most absorption by the small intestine occurs in:

! a) the ileum

! b) the duodenum

! c) the jejunum

Check your answers at the end of this pack.

The large intestine

The food passes through a valve called the ileocaecaecal sphincter into the

large intestine. The large intestine is named because of its width not its

length. Most of the water and any remaining nutrients are absorbed in the

large intestine. The large intestine is made up of two parts:

• The caecum contains microorganisms which digest highly fibrous

material for absorption. The caecum is particularly large in non-ruminant

herbivores such as horses, rabbits and hamsters.

• The colon removes any remaining water in the food.

Rectum and anus

Having passed through the caecum and colon, the remaining waste material

then passes into the rectum, which acts as a storage space. When the rectum

is full, a sphincter opens and allows the remaining waste material to be

ejected through the anus.

The breakdown of proteins, which contain nitrogen, produces ammonia

which is toxic. Mammals convert it into urea which is excreted by the

kidneys. Birds and reptiles convert it into uric acid – a process which needs

less water but uses more energy.


Answers to review quizzes

Review quiz 1

Picture 1 shows a ruminant, while picture 2 shows a simple digestive system.

Review quiz 2

1 C. Sheep are ideal for a new ley as they nibble the grass off very close

to the ground.

2 B. Molars are for grinding.

Review quiz 2

1 A. Hydrochloric acid reduces pH

2 False.

3 B. The small intestine.

Review quiz 3

1 B. The gall bladder secretes bile.

2 C. Bile emulsifies fats.

3 A. Most absorption occurs in the ileum.

Answer to activity on page 6

There are two reasons why an animal needs to grind up its food:

• to produce bits of food small enough to be swallowed easily

• to increase the surface area of the food. This means there is a greater area

to absorb and be affected by digestive chemicals.

Answer to activity on page 7

The distance around the top lump is 12cm, whereas the total distance

around the bottom four is 6x4cm = 24cm.


Further reading

R. D. Frandson, Anatomy and Physiology of Farm Animals (6th Ed).

Lippincolt, Wiley Blackwell, 2003

D.R. Lane and B Cooper, Veterinary Nursing (3rd edition). Butterworth

Heinemann, 2003

William O Reece, Functional Anatomy and Physiology of Domestic Animals

(3rd Ed) Wiley Blackwell, 2004

Glossary

Buccal Cavity The mouth

Caecum Part of large intestine

Colon Part of large intestine

Duodenum First part of small intestine

Echymel Food leaving the stomach

Ileocaecal sphincter Valve between small and large intestine

Ileum Third part of small intestine

Jejunum Second part of small intestine

Monogastric Animal with a simple stomach e.g. pig

Oesophagus Tube leading from mouth to stomach

Peristalsis Muscle action which moves food through the

digestive tract

Pyloric sphincter Valve at bottom of stomach

Ruminant Animal with a complex stomach e.g. cow


Knowledge quiz

1 What is the term for the continuous tube that runs from the mouth to

the anus?

2 What is the main difference between ruminants and non-ruminants?

3 How do the teeth aid digestion?

4 Name the three parts of the small intestine.

5 What is the term for the waves of muscle contraction which move food

along the small intestine?

6 Why does the acid from the stomach need to be neutralised?

7 What does the colon do?

8 Where does the waste material go after it has left the large intestine?

9 What structures line the ileum and help to maximise absorption?


Acknowledgements This learning pack has been produced by the Land Based Colleges National Consortium Ltd.

The LBCNC is a consortium of colleges working in the land-based sector which co-operate in the development and production of quality flexible learning materials which encourage independent learning.

We would like to acknowledge the contributions made by the following individuals and colleges in the development of this learning pack.

Initial source material and guidance

Source material was provided by:

Eirwyn Jenkins, Hartpury College

Paul Attard and Peter Edwards, Walford College

Graham Corner, Cannington College

Developed and produced for LBCNC by Learners First

Illustrations: Shevanthi De-Silva

Revised in July 2011

© 2011 The Land Based Colleges National Consortium Ltd. All rights reserved.

Permission to photocopy or adapt the material in this learning pack is granted to members of the Land Based Colleges National Consortium Ltd. only.

For further information please contact the LBCNC project management team at 7 Tyne Road, Bishopston, Bristol BS7 8EE.

Tel 0117 942 3504

farm animal biological systems - .global - digestion in non-ruminants.pdf · farm animal biological...

Documents