Significance of Forage Analysis Results
noted, the following information pertains to ruminants, cattle in
Moisture the percent water in a sample.
Dry matter equals (100% - Moisture) and represents
everything in the sample other than water including protein, fiber,
fat, minerals, etc.. Animals consume feeds to meet their dry matter
needs, because it is the dry matter that contains all of the nutrients.
Therefore, animals will have to consume more of a wetter feed to
receive the same amount of dry matter as they would from a drier
feed. For example, if an animal consumes 20 lbs. of hay at 90% dry
matter, it consumes 18 lbs. of dry matter (20 x .90). If haylage
at 40% dry matter was to be substituted for the hay, it would have
to consume 45 lbs. of haylage (18/.40) to receive the same amount
of dry matter.
Thus, it is very important to know the dry matter content of a feed
to establish feeding rates and insure that livestock receive the
proper amount of feed to meet their daily needs.
As Sampled Basis nutrient results for the sample in
its natural state including the water. Also known as as fed or as
Dry Matter Basis nutrient results for the sample with
the water removed. There is considerable variation in the moisture
content of forages. Removing the water eliminates the dilution effect
of the water thereby enabling direct comparisons of nutrient contents
across different forages. For example, suppose that you wanted to
compare the protein content of a hay testing 90% dry matter to a
haylage testing 40% dry matter. On an as sampled basis the hay tested
14% crude protein (CP) and the haylage 8% CP. The hay appears to
have the higher CP level. However, removing the dilution effect
of the water reveals that the hay is 15.5% CP (14/.90) and the haylage
is 20% CP (8/.40) on a dry matter basis. Thus, removing the dilution
effect of the water revealed that per pound of dry matter, the haylage
is higher in protein. Animals eating the haylage will consume more
protein per pound of dry matter than they will from the hay.
Livestock nutrient requirements may be expressed on either an as
sampled or dry matter basis. It is important to use analytical results
expressed on the same basis as the nutrient requirements. In general,
most livestock requirements are expressed on a dry matter basis,
therefore, the forage results on a dry matter basis should be used
to balance the ration. Again, the key point is to make sure that
the requirements and results are expressed on the same basis.
and Protein Fractions
Crude Protein (CP) the total protein in the sample
including true protein and non-protein nitrogen. Proteins are organic
compounds composed of amino acids. They are a major component of
vital organs, tissue, muscle, hair, skin, milk and enzymes. Protein
is required on a daily basis for maintenance, lactation, growth
and reproduction. Proteins can be further fractionated for ruminants
according to their rate of breakdown in the rumen.
Urea and Ammonia reported as crude protein equivalent
(CPE). Urea and ammonia are not proteins. However, they contain
nitrogen that can be used by the microbial population in the rumen
to synthesize protein. They are classified as non-protein nitrogen
(NPN). Thus, although they are not true proteins, they supply nitrogen
which can be used to form microbial protein and therefore have a
certain value that is equivalent to protein for ruminants. The reported
result is the CPE contribution from each of these compounds. The
results are not the percent urea or ammonia in the feed. The actual
percentage in the feed can be calculated by dividing the urea CPE
by 2.81 or the ammonia CPE by 5.15. The urea and ammonia appear
in the soluble protein fraction of the protein.
Soluble Protein (SP) proteins and non-protein nitrogen
that are rapidly broken down in the rumen. They are used to synthesize
microbial protein in the rumen.
Degradable Protein (RDP) consists of the soluble protein
and proteins of intermediate ruminal degradability. They are used
to synthesize microbial protein in the rumen.
Undegradable Protein (RUP) proteins that have a slow
rate of degradability and escape digestion in the rumen. UIP is
also known as escape or bypass protein and reaches the lower gastrointestinal
(GI) tract essentially intact. The undegradable protein is broken
down in the GI tract as it would be in nonruminants.
Acid Detergent Insoluble Crude Protein (ADICP) also
known as heat damaged or unavailable protein. Typically caused by
heating during fermentation or drying, a portion of the protein
reacts with carbohydrates to form an indigestible complex rendering
it unavailable for digestion. ADICP escapes ruminal breakdown and
represents the portion of the undegradable protein that is unavailable
to the animal.
Neutral Detergent Insoluble Crude Protein (NDICP)
it has been suggested that the NDICP represents the portion of the
undegradable protein that is available to the animal.
Neutral Detergent Fiber (NDF) a measure of hemicellulose,
cellulose and lignin representing the fibrous bulk of the forage.
These three components are classified as cell wall or structural
carbohydrates. They give the plant rigidity enabling it to support
itself as it grows, much like the skeleton in animals. Hemicellulose
and cellulose can be broken down by microbes in the rumen to provide
energy to the animal. NDF is negatively correlated with intake.
Acid Detergent Fiber (ADF) a measure of cellulose
and lignin. Cellulose varies in digestibility and is negatively
influenced by the lignin content. As lignin content increases, digestibility
of the cellulose decreases. ADF is negatively correlated with overall
Lignin undigestible plant component. Lignin has a
negative impact on cellulose digestibility. As lignin content increases,
digestibility of cellulose decreases thereby lowering the amount
of energy potentially available to the animal.
Crude Fiber (CF) historical method of fiber analysis
used to divide carbohydrates into digestible and indigestible fractions.
Crude fiber accounts for most of the cellulose and only a portion
of the lignin. It is not the most accurate method for quantifying
fiber, particularly for forages. However, given that grains are
low in lignin, it is a reasonable estimate of fiber in grains and
is still used today as the legal measurement of fiber in grains
and finished feeds.
Pectin a cell wall polysaccharide that functions as
"cellular glue". Also known as "soluble fiber",
it possesses the rapid and extensive degradation characteristics
of nonstructural carbohydrates, yet without the propensity to lower
rumen pH or cause lactic acidosis.
Starch a polysaccharide found primarily in the grain
or seed and/or root portions of plants. Starch is a good source
Water Soluble Carbohydrates (WSC) carbohydrates solubilized
and extracted in water. Includes monosaccharies, disaccharides and
some polysaccharides (mainly fructan). Fructan is a major storage
carbohydrate in grasses.
Ethanol Soluble Carbohydrates (ESC) carbohydrates
solubilized and extracted in 80% ethanol. Includes primarily monosaccharides
Non Fiber Carbohydrates (NFC) non-cell wall carbohydrates
consisting of starch, sugar, pectin and fermentation acids that
serve as energy sources for the animal. In ruminants, NFC are broken
down by the microbial population in the rumen and used as an energy
source. NFC is calculated as 100% - (CP% + (NDF% - NDICP%) + Fat%
Fat typically determined by ether extraction. In addition
to fat, ether extraction may solubilize plant pigments, esters and
aldehydes. This is why the measurement is called crude fat. Fat
is an energy dense nutrient and contains 2.25X to 2.8X the energy
found in carbohydrates. Fat is added to rations to boost energy
levels when intake may be limiting.
Energy is the nutrient required in the greatest amount. Energy is
used in all biological processes and is essential for life. For
livestock, energy requirements are determined for maintenance, growth
or gain, lactation, reproduction and activity level. Failure to
supply adequate energy will result in poor performance. Energy values
are not measured, rather they are predicted using equations and
relationships with other nutrients. Dairy One uses a multiple component
summative approach for its ruminant energy prediction system. Energy
contributions from protein, fiber, nonstructural carbohydrates and
fat form the foundation of the system. Discounts are applied to
reflect energy available for productive purposes.
Total Digestible Nutrients (TDN) denotes the sum of
the digestible protein, digestible NSC, digestible NDF and 2.25X
the digestible fat.
Gross Energy the total energy value of a feed before
accounting for losses due normal digestive, metabolic and productive
Digestible Energy (DE) equals gross feed energy minus
energy lost in the feces.
Metabolizable Energy (ME) equals gross feed energy
minus energy lost in the feces, urine and gases.
Net Energy for Lactation (NEl) an estimate of the
energy value of a feed used for maintenance plus milk production
during lactation and for maintenance plus the last two months of
gestation for dry, pregnant cows.
Net Energy for Maintenance (NEm) an estimate of the
energy value of a feed used to keep an animal in energy equilibrium,
i.e., neither gaining or losing weight.
Net Energy for Gain (NEg) an estimate of the energy
value of a feed used for body weight gain above that required for
SS NEl corn silage NEl value adjusted for starch digestibility
using the Schwab-Shaver adjustment factors.
SS Proc. NEl corn silage NEl value adjusted for starch
digestibility as described above plus the effect of whole plant
NRC 2001 Energy Table energy values determined using
the system described in the 2001 NRC Dairy Cattle publication. The
NEl table reflects the decline in energy value of a feed associated
with increasing levels of milk production, dry matter intake and
rate of passage.
Total Digestible Nutrients (TDN) denotes the sum of
the digestible protein, digestible nitrogen-free extract (NFE),
digestible crude fiber and 2.25X the digestible fat. TDN is estimated
from digestible energy (DE).
Digestible Energy (DE) equals gross feed energy minus
fecal energy. It is predicted from ADF and CP for forages and ADF
Ash a measure of the total mineral content. Samples
are weighed and incinerated at 600oC for two hours. This burns off
all of the organic material (protein, fiber, fat, etc.) leaving
behind the minerals. The ash residue weight is then divided into
the original weight to determine the percent ash.
Calcium (Ca) bone and teeth formation, blood clotting,
muscle contractions, milk component, transmission of nerve impulses,
cardiac regulation, activation and stabilization of enzymes.
Phosphorus (P) bone and teeth formation, key component
of energy metabolism, milk component, body fluid buffer systems.
Magnesium (Mg) enzyme activator, found in skeletal
tissue and bone, neuromuscular transmissions.
Potassium (K) osmotic pressure regulation and water
balance, electrolyte balance, acid-base balance, enzyme activator,
muscle contraction, nerve impulse conductor.
Sodium (Na) Acid-base balance, muscle contraction,
nerve transmission, maintenance of body fluid balance, osmotic pressure
regulator, cellular uptake of glucose, amino acid transport.
Iron (Fe) hemoglobin and oxygen transport, enzyme
Zinc (Zn) enzyme activator, wound healing, skin health,
some impact on udder health (reduced somatic cell counts (SCC)).
Copper (Cu) required for hemoglobin synthesis, coenzyme
Manganese (Mn) growth, bone formation, enzyme activator,
Molybdenum (Mo) part of enzyme xanthine oxidase, antagonistic
and interactive effects with copper and sulfur.
Sulfur (S) needed for microbial protein synthesis,
especially when non-protein nitrogen (NPN) is fed.
Chloride (Cl-) acid-base balance, osmotic pressure
regulation, component of gastric secretions.
Cobalt (Co) required for vitamin B12 synthesis.
Selenium (Se) component of glutathione peroxidase
enzyme, antioxidant properties, prevention of white muscle disease
and retained placenta.
In Vitro True Digestibility (IVTD) an anaerobic fermentation
performed in the laboratory to simulate digestion as it occurs in
the rumen. Rumen fluid is collected from ruminally cannulated high
producing dairy cows consuming a typical total mixed ration (TMR).
Forage samples are incubated in rumen fluid and buffer for a specified
time period at 39oC (body temperature). During this time, the microbial
population in the rumen fluid digests the sample as would occur
in the rumen. Upon completion, the samples are extracted in neutral
detergent solution to leave behind the undigested fibrous residue.
The result is a measure of digestibility that can be used to estimate
Neutral Detergent Fiber Digestibility (NDFD) The proportion
of NDF potentially available as determined by an in vitro incubation.
NDFD is expressed as a percentage of the NDF. The NDFD can be used
to rank forages on potential fiber digestibility and in energy calculations.
Relative Feed Value (RFV) an index for ranking forages
based on digestibility and intake potential. RFV is calculated from
ADF and NDF. A RFV of 100 is considered the average score and represents
an alfalfa hay containing 41% ADF and 53% NDF on a dry matter basis.
The higher the RFV, the better the quality.
Due to the inherent variability of measuring ADF and NDF, absolute
RFV values should not be used for making direct comparisons or pricing
of forages. Rather a range of RFV values should be used to classify
a forage. For example, if a RFV of 150 is the target value, any
forage testing between 145 to 155 should be considered to have an
equivalent value. A good rule of thumb is to accept anything within
at least +/- 5 points of the target value.
Relative Forage Quality (RFQ) an index for ranking
forages based on a more comprehensive analysis than RFV. RFQ is
calculated from CP, ADF, NDF, fat, ash and NDF digestibility measured
at 48 hours. It should be more reflective of the feeding value of
the forage. RFQ is based on the same scoring system as RFV with
an average score of 100. The higher the RFQ, the better the quality.
Milk lbs./ton a projection of potential milk yield
per ton of forage dry matter based on digestibility and energy content
of the forage.
Nitrates (N03) can be come a problem when fed in high
amounts. Nitrate accumulator plants include sorghum, sorghum sudangrass,
sudangrass, weeds and small grain forages. Drought, frost, fertilization
and manure application practices are factors that can lead to high
nitrate levels. Drought stricken corn silage is particularly susceptible.
Nitrates accumulate in the bottom portion of the stalk and it is
often recommended that suspect corn silage be chopped higher than
usual. Nitrate levels may be reduced by up to 50% by ensiling.
When nitrate is converted to nitrite, it impedes the uptake of oxygen
by the blood resulting in death due to lack of oxygen. Blood becomes
brownish in color and exterior membranes may become bluish in color.
pH a measure of the degree of acidity. Good corn silage
typically has a pH of 3.5 - 4.5 and haycrop silages 3.8 - 5.3.
Volatile Fatty Acids (VFA) primarily lactic, acetic,
propionic and butyric acids produced as a result of microbial fermentation
in silage or the rumen.