Senwes Scenario December 2018 / January 2019 | Page 23

AGRICULTURAL
presented only with a percentage of ani-
mals although all the animals have been
exposed to the infection.
WHAT IS THE NUTRITIONAL
REQUIREMENTS OF STRESSED
ANIMALS?
Acute (immediate) or prolonged (two to
seven days) stress makes animals more
susceptible to disease. Stressful stimuli in
cattle include handling, transport, physical
trauma, fatigue, fasting, and unfamiliar
environment. Increasing levels of hor-
mones like cortisol, epinephrine, norepi-
nephrine, aldosterone, beta-endorphin,
and encephalin are released during stress.
These induce hormonal responses which
control and alter animal metabolism hor-
mones, suppress the immune system by
depleting nutrients critical to an effective
immune response. Metabolic pathways
shift from anabolic processes (growth) to
primarily catabolic (tissue breakdown of
proteins and fat).
WHAT IS THE EFFECTS OF DISEASE
ON NUTRITIONAL STATUS?
Infection results in a complex array of
metabolic responses which affect the
nutritional status of the animal. Feed intake
decreases more than 50% in cattle with
respiratory disease and fever, and takes
10 to 14 days to return to normal. During
this time, requirements of virtually all
nutrients increase, even though nutrients
are deflected from growth to immunity.
Proteins must be synthesized for the
immune response, development and reso-
lution of fever, and repair of cell and tissue
damage. Body proteins are broken down
to provide energy and amino acids for
the immune system. Losses of important
minerals such as magnesium, potassium,
phosphate, and zinc are also increased.
The major extracellular electrolytes,
sodium and chloride, are influenced by
hormonal changes. Urinary excretion of
salt may increase during the onset of infec-
tion, and may lead to dehydration. The
kidneys may then begin to retain body salt
and water. Diarrhoea can result in substan-
tial direct faecal losses of sodium, chloride,
bicarbonate and potassium.
The immune system appears to have
priority for nutrients over growth. Immune
activation is costly. Resources devoted
to immune activation cannot be used for
growth. As a result, any immune response
will depress growth rate and feed efficien-
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SENWES SCENARIO | TECHNOLOGY & INNOVATION 2018
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