Theme:
im
An al feed
AGRICULTURAL
ROUGHAGE
IN THE FEEDLOT
What is the value of roughage and how is it
utilized in feedlot diets?
Ruminants such as cattle and sheep, evolved as forage consumers. To maintain a healthy
digestive system a minimum level of roughage needs to be included in a feedlot feed.
Different sources of roughage have various nutritional value and physical characteristics
which must be taken into account in formulating feedlot rations.
By Dr Kobus Swart
Animal Nutrition Specialist
P
lant cell walls, which we measure
as fiber, cannot be digested by
animals, but must be fermented
by micro-organisms. Ruminants
swallow large particles of forage and
selectively retain them in the rumen to
allow adequate time for fermentation.
They ruminate to enhance digestion and
allow passage through the digestive tract.
During chewing, they produce salivary
buffers that help to maintain the pH in the
rumen.
In animal production systems there
are economic, operational and nutritional
reasons for limiting the forage or roughage
10
SENWES SCENARIO | WINTER 2019
content in feedlot rations. Economically,
grains and concentrate feeds often are
less expensive sources of nutrients than
forages. Operationally, roughages create
difficulties and additional expense in
processing (chopping or grinding), in
uniformly mixing and delivering rations,
and in obtaining consistent intakes without
sorting. Nutritionally, roughages tend to
be more variable in nutrient content, which
also makes it difficult to use them in rations
with consistent results. Thus, there are
many practical reasons for minimizing for-
age in rations of feedlot cattle.
MEASURING FIBER IN FEEDS
FOR RUMINANTS
In animal feeding, fiber is a term used
to define a nutritional, not a chemical or
plant anatomical concept. Nutritionally,
fiber has both physical and chemical
attributes that are related to the mechani
cal processes of digestion (chewing and
passage) and to enzymatic degradation
associated with fermentation.
The fiber with the smallest magnitude
is crude fiber (CF), is not an accurate
prediction of fiber and is not used any-
more. As acid detergent fiber (ADF) does
not contain hemicellulose, it is not an
accurate estimate of fiber in feeds. ADF
recovers most, if not all, of the polymeric
lignin and cellulose in feeds, with some
contamination from pectin, hemicellulose,
tannin-protein complexes, and ash. Only
neutral detergent fiber (NDF) isolates all of
the insoluble fiber components in plants
(hemicellulose, cellulose, and lignin) with