Body Systems
Session 5 - The Excretory System and the Removal of Waste
This resource is suitable to support Level 2 Agriculture courses.
The Excretory System and the Removal of Waste
The excretory system removes waste products from the animal.
The gut removes the indigestible waste products of digestion
directly from the digestive tract through the anus.
Other waste passes from the tissues into the bloodstream and is
removed from the blood by the liver and kidneys.
The Lungs
The lungs enable the body to remove the waste products of
respiration, namely carbon dioxide and water, by expiration.
The Liver
The liver has many functions, these include:
Making bile from damaged red blood cells.
Breakdown excess amino acids into urea which is released into the
bloodstream to be removed by the kidneys.
The removal of toxic substances from the blood e.g. alcohol.
Breakdown of body fat reserves to release energy (this can
occasionally cause the release of toxic chemicals (ketones) and
result in ill health e.g. twin lamb disease in pregnant ewes).
The Kidneys
The body has two kidneys and these filter the blood.
They remove excess salts, water and urea from the blood and collect
the resulting urine which is then passed to the bladder through the
ureter.
The urine is stored in the bladder before being passed out of the
body through the urethra.
Temperature Control
Cattle, sheep and pigs are mammals.
They are warm blooded animals so they have body systems which can
regulate their temperature.
Average body temperatures are :
Cattle = 38.9 °C
Sheep = 40.0 °C
Pigs = 39.7 °C
Heat Loss
Animals lose heat by panting or sweating, both of these actions will
increase their water requirement.
They will also take action to cool down if possible e.g. seeking
shade, standing in streams.
Sweating is an active process that requires heat to evaporate water,
taking heat from the skin to evaporate water cools the animal. To
increase the amount of heat loss, animals can increase the blood
flow to the skin.
Effect of Increased Body Heat on Animals
If the environment is too hot then feed intake decreases and
production will be reduced e.g. reduced milk yield in dairy cows.
Temperatures can vary widely over a 24 hour period, so animals which
have been too hot and sweated during the day may then be damp and
cold later if the sweat has not evaporated.
Maintaining and Producing Heat
Adult sheep and cattle with full coats or fleeces can maintain their
temperature as long as they have sufficient feed and shelter.
Young animals have a relatively large surface area (a large amount
of skin surface compared to their volume) and lower fat reserves so
they are more at risk from hypothermia (being too cold).
How Do Animals Generate Heat?
Animals can generate heat by breaking down fat; very young animals
only have a small fat reserve so they need colostrum (and later
milk) to provide them with the energy to keep warm.
If animals become wet through they will lose heat more rapidly
because of the energy taken from their skin to evaporate the water.
Effect of Coat Type on Heat Loss
The amount and type of birth coat will also affect the young
animal’s ability to keep warm. Hill lambs are born with thick birth
coats that will protect them from the weather.
Piglets only have very fine hair, so they need protection from the
elements; outdoor systems have bedded arcs for sows and piglets,
many indoors systems have heated creep areas.
In older animals the coat varies according to the breed and the
level of feeding that the animal receives.
How Can Animals Increase Their Body Heat?
Other mechanisms used to keep warm are shivering, making hairs erect
and reducing blood flow to the skin.
The rapid movement of muscle when shivering will produce body heat;
however animals can be suffering from hypothermia but not shivering.
Making the hairs erect will trap more air close to the skin to
insulate the animal. Constricting the blood vessels near the skin
will reduce the skin temperature and the amount of heat lost.
Problems in the Excretory System
Problems in the Excretory System
Urinary calculi
These are crystals that form in the urine due to its high mineral
content.
These may block the urethra so that the animal is unable to pass
urine.
It usually occurs in castrated lambs fed on concentrates.