Senwes Scenario December 2018 / January 2019 | Page 22

AGRICULTURAL
Nutrition and Immunity
of Feedlot Cattle
Is special handling and nutrition necessary?
A healthy animal give the best production results and a sick animal causes directly and
indirectly unnecessary costs. The immune system accounts for a minor portion of total
nutritional requirements in the healthy animal but in response to an immune challenge
has a major impact on nutritional status and requirements for specific nutrients.
 By dr Kobus Swart
Animal Nutrition Specialist
N
utrient deficiencies increase
susceptibility to most infec-
tious diseases and increase
the probability of secondary
infections. Vitamins or trace minerals
deficiencies significantly depress immune
function and resistance to stress even
when animals are otherwise well fed with
sufficient energy and protein. Nutrition
has the largest impact on morbidity and
mortality during the first month after arrival
at the feedlot.
WHAT IS THE PROBLEM?
The immune system is suppressed in
stressed cattle, contributing to the high
incidence of respiratory disease in the first
30 to 45 days on feed. Lungs of healthy
cattle can resist challenge from surprising-
ly large numbers of bacteria. But when the
animal is stressed, relatively small num-
bers of bacteria can result in pneumonia.
20
An additional aspect during this early
stage is to adapt the rumen to easy
digestible (starch) feed. If this process is
not managed well, metabolic disturbances
(acidosis) can easily occur. This causes
a decline in intake, permanent damage
to the rumen wall, dehydration and poor
digestibility of ingested feed which impos-
es a huge challenge to the immunity of
the animal.
Nutrition has the greatest impact
on immunity during the first two to four
weeks after arrival at the feedlot, even
more so in the first few days after arriv-
al. A problem is to get enough nutrients
into cattle, particularly those that need
it the most. Providing key nutrients can
reduce stress-induced weight loss and
immune suppression, improve weight gain
and reduce morbidity and mortality from
bovine respiratory disease.
WHAT IS IMMUNITY TO INFECTION?
Animals resist infection using non-specific
mechanisms (‘innate’ immunity) and spe-
cific mechanisms (acquired immunity).
SENWES SCENARIO | TECHNOLOGY & INNOVATION 2018
Innate immunity includes epithelial tissue
which covers body surfaces (example
skin or hide, hoof, cornea) and lines body
cavities (respiratory, urogenital, gas-
tro-intestinal) is a physical barrier to keep
infectious agents from entering the body.
Acquired immunity is where exposure
to a foreign substance (antigen) results
in the development of immune cells and
antibodies specific against that particular
antigen only. Specific immunity takes time
to develop, and therefore is effective in
preventing infection only if the animal was
previously exposed to that antigen.
A nutrient deficiency does not affect all
immune mechanisms equally, nor does
it always affect the same mechanism
equally for different antigens. A group
of deficient animals may have adequate
antibody responses to some antigens
(or vaccines), and depressed antibody
responses to other antigens. Similarly,
under practical conditions, deficient ani-
mals may be more susceptible to some
but not all disease causing organisms.
That is why the symptoms of disease are