CHO Metabolism
CHO Metabolism
- CHO constitute 70% or
more of the DM
- Major precursor of
energy
- Partitioning CHO into
fiber & non-fiber
CHO Metabolism
Optimal utilization of
diets influenced by:
- Chemical composition
- Physical characteristics
(particle size & density
- Physical characteristics can
influence: animal health,
ruminal fermentation &
utilization, & animal
performance.
- Fiber: Slowly digestible
or indigestible fraction
- NDF measures total
fiber
- NDF relates to: Intake,
feed density, chewing
activity, digestibility,
rate of digestion & milk
fat production
CHO Metabolism
Fiber Chewing
Acid Production
Fiber Chewing
Salivary buffer
Ruminal pH A:P ratio
milk fat
Non-fibrous CHO (NFC)=
100- ( NDF+CP+EE+Ash)
Nonstructural CHO
(NSC)=Analytical method
•NFC NSC
•Lower ruminal pH result
of too much NFC or NSC
Neutral Detergent Soluble CHOH
A calculated value:
NDSC = 100 -
(%NDF+%CP+%Fat+%Ash)
NDF corrected for protein
• 98% potentially digestible in the
rumen
• Rapidly fermented in the rumen
• Diverse group and not easily
measured directly in feeds
• Not all digested by mammalian
enzymes
Effective Fiber
refer to ability of fiber to
maintain milk fat
production and animal
health effectively
Physical effective NDF
(peNDF)=
related to physical
characteristics of fiber
(primarily particle size) that
influence chewing activity
and the biphasic nature of
ruminal contents (floating
mat of large particles on a
pool of liquid and small
particles)
Pe NDF relates only to the
physical properties of fiber
•peNDF is a more restricted
term and concept than NDF
•peNDF of a feed is the
product of its NDF
concentration and its
physically effectiveness
factor (pef)
•Pef varies from 0, when
NDF is not effective in
stimulating chewing
activity, to 1 when NDF
is fully effective in
promoting chewing
peNDF is related to animal health
and milk fat depression, because
ruminal pH and the pattern of
fermentation is a function of:
production of salivary buffers
during eating and rumination.
•Chewing activity / Kg DM
varies with: 1) breed, 2) size,
3) level of intake, 4) fiber
content, and 5) particle size.
•The animal response that is
associated with eNDF is milk
fat percentage.
•Effectiveness factor for NDF
can vary from 0, when a feed
has no ability to maintain milk
fat percentage , to values
greater than 1.0 when a feed
maintain milk fat percentage
more effectively than it
maintain chewing activity.
CHO Metabolism
Logically peNDF and
eNDF should be highly
correlated
eNDF can be greater
than peNDF for feeds
that maintain milk fat
percentage but do not
stimulate chewing
activity to a similar
extent (e.g., feeds
containing fats or
intrinsic buffering
capacity).
•Conversely, eNDF can be less
than peNDF for feeds that
detrimentally affect ruminal
fermentation and milk fat
production without affecting
chewing activity (e.g., feeds
containing sugars).
•Non-fiber facotrs of feeds
that influence milk fat
synthesis are included in
eNDF, but not peNDF.
•Because eNDF is related to
intrinsic pH buffering and
neutralizing capacity, fat
concentration and
composition, acid producing
during fermentation, pH
changes reflecting the
balance of buffering capacity
and acid production, shift in
VFA amounts and ratio
produced, and metabolic
changes that influence
secretion of milk fat
Laboratory
assessment of
fiber
effectiveness
NDF method proposed
by Robertson and Van
Soest
Particles retained on a
1.18 mm sieve have a
high resistance to
passage from the
rumen of both cattle
and sheep
•A simple system for
estimating peNDF from
chemical and physical
measurements in the
laboratory can be based
on NDF concentration
and the proportion of
particles that are
retained on a 1.18 mm
sieve.
•Another method for
estimating eNDF is using Pen
state separator
Biological
Assessment of
Fiber Effectiveness
First step is developing a
scale for assessing pe is to
define a reference against
which all feeds are
compared
A hypothetical std that would
result in the max amount of
chewing/ Kg DM or NDF.
The reference feed should be
a long grass hay containing
100% NDF that is assigned a
pef of 1.0 resulting in a peNDF
of 100.
•Chewing/ Kg of NDF
increase as the NDF in
long forage increase
(Table 1).
•Particle size reduction
decrease chewing
activity/ Kg NDF (Table 2).
•Chopping forages to 4 cm
reduced total chewing
activity to 80% of the
unchopped forage.
• Grinding forage reduce
chewing activity to 20-60%
of that for long forage.
Measurement of in
vivo digestion
kinetics
Total tract
digestibility
direct: total fecal
collection
indirect:markers
CHO Metabolism
peNDF is related to fiber
concentration, particle size, and
particle size reduction, so
peNDF is related to the
formation of ruminal mat, which
may be a critical factor for
selectively retaining fiber in the
rumen, determining the
dynamics of ruminal
fermentation and passage and
stimulating rumination.