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Overview of animal digestive systems
Do you think all that the digestive systems for all animals are the same? You
are right, if you said ‘No’. Having a basic understanding animal digestive
systems will give you more knowledge about the type of foods that are good
for them. How animals obtain different nutrients will depend on their
digestive systems.
Types of digestive systems
The main types of digestive system types include:

simple monogastric

complex monogastric

ruminant

avian.
Simple monogastric
Examples of animals with simple monogastric systems include dogs, cats,
ferrets, the Tasmanian devil and small carnivorous marsupials. Simple
monogastric animals have a simple stomach and a relatively short large
intestines. They obtain their nutrients from eating meat and/or invertebrates,
which are relatively easy to digest.
Figure 1: Border collie–example of animal with simple monogastric system
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© NSW DET 2007
Complex monogastric
Examples of animals with complex monogastric systems are rabbits, guinea
pigs, horses, possums and koalas. In complex monogastric animals, the
digestive system is modified for a plant, or herbivorous diet. This means the
modification of:

the teeth, for grinding rather than tearing–canine's teeth may be
absent or not functional

the large intestine, or caecum and colon, to allow for longer passage
of food and some bacterial and protozoal fermentation.
Some animals eat their faeces (coprophagy), and it is common for young
animals to eat their mother’s faeces, to help them get the necessary bacteria
and protozoa.
Figure 2: A koala–example of animal with complex monogastric system
Ruminant
Examples of animals with ruminant systems are cattle, sheep and goats.
Kangaroos also have a similar digestive system. In the ruminant system,
there are four stomachs:

The rumen or paunch–the largest stomach on the left side of the
abdomen. It’s lining looks like carpet.

The reticulum or honeycomb tripe–the most cranial stomach. It acts
as a grinding and mixing organ. There is a groove called the
oesophageal groove that allows food to pass directly from the
oesophagus to the reticulum.
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© NSW DET 2007

The omasum or bible–looks like pages of a book. It squeezes water
out of the contents.

The abomasum or true stomach–the equivalent of the monogastric
stomach, containing acid and digestive juices.
Animals digestive systems are modified in the following ways:

The tongue and lips are modified for collecting and tearing plant
material such as grasses and branches.

The teeth are designed for grinding, and often continue growing
throughout life.

There is often a gap, called a diastema between the incisors and the
premolars, which allows the tongue to move the food around.

Some ruminants lack upper incisors, instead having a hard ‘dental
pad’.

The salivary glands produce large quantities of saliva to help
swallow hard fibrous food.
Figure 3: Bradford bulls have a ruminant system
Avian
Birds have a modified digestive system in the following ways:

They have a beak but not teeth.

They have a crop, or storage area in the oesophagus.

They have two stomachs -a normal stomach, called the
proventriculus, and a grinding stomach called the gizzard.

Some birds have twin caecae.
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© NSW DET 2007
Figure 4: Cormorants have a modified digestive system
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© NSW DET 2007