Quality and Feeding
Feeding silage
Silage evaluation
Quality of corn silage is determined by energy content and intake
potential as well as content of protein and minerals. Methods used to
evaluate corn silage quality include chemical methods such as fiber
analysis, biological methods such as fermentation with ruminal microbes,
and instrumental methods such as near-infrared reflectance spectroscopy
(NIRS) which predicts nutrients rather than measuring them directly.
All methods require that the sample being analyzed is representative of
the silage that is being offered to the animal. Therefore,
representative samples must be obtained from the silo and the samples
must be handled properly prior to analysis. Corn silage samples should
be sealed in a plastic bag and sent to a laboratory as soon as possible
to reduce spoilage. Care should be taken to avoid exposure of the sample
to high temperatures. Samples of fresh forage which are taken when the
silo is being filled must be dried immediately to reduce losses due to
respiration of sugars, which can dramatically increase the
concentration of the remaining nutrients. Do not freeze samples as the
fiber content becomes artificially increased during thawing due to the
condensation of soluble protein with other compounds.
METHODS FOR DETERMINING ENERGY CONTENT
The energy content of corn silage is primarily determined by the amount
and digestibility of fiber. Grain content also affects energy content,
although it is possible for a corn silage with less than 30% grain to
have a higher energy content than a corn silage with more than 50% grain
due to differences in stover digestibility. Starch digestibility affects
energy content for dry corn silages but is less of a factor for corn
silage with greater than 60% moisture. As determining digestibility
using animals (in vivo digestibility) is too time consuming and
expensive for routine use, several techniques are used to estimate
digestibility and energy content.
Total digestible nutrients (TDN) describes the energy
content of feeds as the sum of the digestibilities of different
nutrients. However, because animals use the available energy differently
depending on the
feed and on the animal's production status, the TDN system overestimates
energy derived from forages relative to grain. Appendix table 4 presents
commonly used energy estimates.
The net energy system accounts for the variation in
digestible energy usage by assigning feeds three net energy values: net
energy for maintenance (NEm)' net energy for gain (NEg), and net energy
for lactation (NEL). Digestible energy used for maintenance and for milk
production is used more efficiently than digestible energy used for
gain. While equations convert TDN energy values to NE values, the same
equation is usually used for both forages and grains, which decreases
accuracy.
The acid detergent fiber (ADF) content of silage is the
most common method used by commercial feed testing laboratories to
predict energy content. As ADF decreases, the digestibility and
therefore the energy content increases. This method offers low cost and
rapid turnaround, which are requirements for balancing animal rations.
ADF contains lignin (totally indigestible) as well as cellulose (poorly
digestible) and pectin (highly digestible). The relationship between ADF
and energy content is not absolute, however, since ADF accounts for less
than two-thirds of the variation in energy content in corn silage. The
inaccuracy of this method is caused by significant variations in the
digestibility of the fiber in corn silage.
In vitro digestibility methods use fermentation by
ruminal microbes in test tubes or artificial rumens to determine
digestibility. In situ digestibility methods allow forage digestion
inside the rumen of a cow or steer. These methods offer greater accuracy
of energy prediction because they account for variation in fiber
digestibility but are more time consuming and expensive than ADF
determination. Due to cost and complicated procedures of in vitro
techniques, they are used primarily for research purposes such as hybrid
comparison. However, near-infrared reflectance (NIRS) equations
accurately estimate in vitro values, allowing ranking of commercially
available hybrids.
Table 11. Average composition of poor and well-eared corn silage.
Component |
Well-eared (%) |
Poor (%) |
Crude protein |
8.6 |
8.4 |
NDF |
46.0 |
53.0 |
ADF |
26.0 |
30.0 |
Cellulose |
22.0 |
23.0 |
Lignin |
4.0 |
5.0 |
Ash |
3.0 |
7.2 |
Calcium |
0.30 |
0.34 |
Phosphorous |
0.28 |
0.19 |
Potassium |
1.32 |
1.41 |
SILAGE COMPOSITION
FORAGE QUALITY TERMS
NDF (neutral-detergent fiber). A measurement of the
total fiber content of a forage. NDF is composed of cellulose,
hemicellulose, and lignin. High fiber forages fill the stomach faster,
meaning the animal
eats less and needs more ration supplements. Corn silage NDF
concentration ranges from 36 to 50%. A low corn silage NDF is desirable.
ADF (acid-detergent fiber). A measurement of the
cellulose, lignin, and pectin fiber fractions of forages. ADF is
commonly used to predict energy content of corn silage and other
forages. Corn silage ADF concentration ranges from 18 to 26%. Corn
silages with lower ADF values have a higher energy content and are
desirable.
Lignin. An indigestible fiber that has no energy value
to the animal. In addition, lignin restricts digestibility of other
fiber components. The lignin content of corn silage is low and ranges
from about 2 to 4%. A low lignin content is desirable.
In vitro dry maHer digestibility (IVDMD). A measure of
the apparent digestibility of dry matter. Determined by incubating feed
in a flask with ruminal microbes and following this incubation with a
pepsin and hydrochloric acid incubation to simulate digestion in the
true stomach. The amount of dry matter remaining is divided by the
original dry matter and subtracted from 1.0.
In vitro NDF digestibility (or cell wall digestibility).
A measure of ruminal digestibility of NDF. Determined by
incubating feed in a flask with ruminal microbes followed by analyzing
the fiber content of the residue. The amount of fiber content remaining
is divided by the original fiber content and subtracted from 1.0.
In situ dry matter digestibility. A measure of the
apparent digestibility of dry matter. Determined by placing the forage
sample in a dacron bag within the rumen of a cow or steer. The sample is
retrieved, washed, dried, and weighed. The amount of dry matter
remaining is divided by original dry matter and subtracted from 1.0.
In vivo digestibility. A measure of the digestibility
of dry matter using animals. Disappearance of dry matter (digestibility)
is determined as the difference between the quantity of dry matter
consumed
and the quantity of dry matter excreted in the feces.
Energy content. The results of each method can be used
directly to rank: hybrids for digestibility but must be adjusted for
specific feeding situations to accurately predict digestibility and
energy content. The length of time that feeds reside in the rumen and
are fermented varies depending on several factors including animal
species and level of intake. Digestibility increases as fermentation
time increases. In general, animals with high dry matter intakes such as
those that are rapidly growing or producing large quantities of milk,
have shorter ruminal retention times and digest food less efficiently
than animals with lower dry matter intakes.
Consequently, the energy content of corn silage varies depending on the
animal to which it is fed. For instance, a steer at maintenance intake
with a ruminal retention time of over 40 hours will obtain more energy
from the same feed as a high-producing dairy cow with a ruminal
retention time of 30 hours or less. Accuracy of energy prediction also
decreases as corn silage dry matter increases because many corn kernels
pass through the gastrointestinal tract undigested, reducing starch
digestibility. These factors coupled with the environmental effects
cause energy content of corn silage to vary from 62 to 74% TDN or
approximately 0.64 to 0.75 mcal/lb NEL.
Corn silage in vitro NDF digestibility ranges from 30 to 60%. This
variation is primarily due to environmental conditions during crop
growth. However, corn hybrids have been found to differ by up to 5 units
in NDF digestibility and NDF digestibility has been found to decline
with advancing maturity. Variation in NDF digestibility has great
consequences to forage utilization in three different areas: it affects
the energy density of the ration, dry matter intake, and microbial
protein production.
Energy density of the ration is affected because a certain amount of
fiber is required in the ration for normal, healthy rumen function.
Therefore, less energy from this fiber will reduce energy density and
energy intake. Feeds with high fiber digestibility have a lower filling
effect and allow greater intake than feeds with low fiber digestibility.
Differences in fiber digestibility also affect the amount of protein
available to the animal.
Intake potential. High fiber diets fed to ruminants
limit intake due to the filling effect of the food. Fiber (ND F) is
fermented and passed from the rumen slowly compared to nonfibrous feed
components such as sugars and starch. Less digestible fiber is retained
in the rumen longer than highly digestible fiber. Therefore, the filling
property of a forage is related to its NDF content and NDF
digestibility. A low NDF content and high NDF digestibility of corn
silage are desirable to maximize forage and dry matter intake.
The NDF content of corn silage varies by hybrid and climate, and
decreases with nitrogen fertilization and maturity at harvest. It is a
major factor determining corn silage intake for lactating dairy cows in
early lactation. To ensure adequate chewing and salivation,
nutritionists generally balance rations of high-producing cows for an
optimum amount of fiber to maximize energy intake. If too much fiber is
in the ration, intake will be limited and more body condition will be
lost. If there is too little fiber in the ration there will be excess
formation of fermentation acids and inadequate buffering, intake will be
limited and again more condition will be lost. Because of this, meeting
the animal's fiber requirements takes precedence over attempting to meet
the animal's energy requirements. Corn silage with a low NDF content can
be included in the ration at higher levels than corn silage with a high
ND F content.
Protein. Crude protein is a mixture of true protein and
nonprotein nitrogen. Less than 30% of the total protein in corn forage
is available to the animal as absorbable true protein as much of it is
degraded by
fermentation in the silo and in the rumen to nonprotein nitrogen.
However, much of the ammonia produced in the fermentation process is
available to the animal. Some of the crude protein is totally
unavailable to the animal. This fraction is called bound protein or
heat-damaged protein. Although it is usually negligible, this fraction
can be substantial for silages that have heated extensively in the silo
and must be adjusted for when balancing rations. Crude protein levels of
untreated corn silage range from less than 6% to over 10% of dry matter
depending on environmental conditions, fertilization, hybrid, and
maturity.
Feeding silage to dairy cattle
Corn silage is used for feeding all dairy cattle on the farm: growing
animals, dry cows, and lactating cows. It must be supplemented with
protein, minerals, and sometimes energy to meet the animal's nutrient
requirements. Although corn silage is occasionally used as the only
forage for dairy cattle, it is usually fed with a complimentary forage
such as alfalfa which is higher in crude protein but lower in energy.
Corn silage feeding strategies vary depending on animal age, level of
production, and physiological status as well as the other forages being
fed, if any. Because of its high grain content, feeding strategy for
corn silage fed to high producing cows differs from most other forages.
Corn silage quality factors that are important to consider when
balancing rations are energy content, NDF content, NDF digestibility,
length of cut, starch content, and starch digestibility.
HEIFERS AND DRY COWS
Corn silage is an excellent dry cow forage as it is palatable and can be
limit fed or mixed with lower energy forages. However, the amount of
corn silage fed to dry cows and heifers must be restricted due to its
high energy content. Dry cows require rations balanced from 0.57 mcal/lb
NEL early to over 0.72 mcal/lb NEL depending on their body condition and
time until calving. Increase the ration energy density 2 to 3 weeks
before calving as fetal energy requirements increase and the cow's dry
matter intake decreases. Fat cows should receive rations of lower energy
density than thin cows. Feeding unrestricted quantities of corn silage
throughout the dry period will result in fat cows which tend to have
lower dry matter intakes and higher incidence of metabolic problems such
as ketosis and fatty liver following calving. Corn silage contains low
calcium compared to other forages. This is an advantage because high
calcium intake in the dry period contributes to milk fever following
calving.
Corn silage can be fed to replacement heifers beginning at approximately
6 months of age. Energy requirements of growing heifers decreases from
69% TDN at 3 to 6 months of age to 61%TDN for heifers over 12 months of
age. Feeding unrestricted quantities of corn silage to heifers will
result in fat animals with lower potential milk production due to fatty
infiltration of the udder. Restricting feed intake presents a problem
for group-housed heifers because more aggressive animals may receive
more than their share, resulting in uneven body condition among the
heifers in the group. As protein requirements of growing heifers ranges
from over 16% at 3 to 6 months of age to about 14% for heifers over 12
months of age, corn silage must be supplemented with protein when fed to
heifers. A solution to restricted feeding of corn silage to heifers is
to feed a combination of corn silage and a higher protein, lower energy
forage such as a legume silage.
LACTATING DAIRY COWS
The high energy requirements of lactating dairy cows increase the
difficulty of balancing rations that meet animal needs for both energy
and fiber. The effectiveness of corn silage fiber at stimulating rumen
movements and chewing is primarily determined by its length of cut.
Coarsely chopped corn silage will stimulate more chewing and salivation
per pound of fiber than feeding the same silage that has been finely
chopped. If fiber is more effective at stimulating chewing and
salivation, less is needed in the ration to provide the same amount of
buffering from saliva. Although coarsely chopped corn silage is more
effective at stimulating chewing it will not pack as densely in the
silo, will have fewer corn kernel coats broken, and will have larger
pieces of cob which will allow sorting and possibly refusal by cows than
more finely chopped corn silage. Length of cut should be adjusted to
provide larger silage particles while minimizing the number of large cob
particles and unbroken corn kernels. Wetter corn forage can be chopped
coarser than drier corn forage. Dry corn kernels require a finer chop to
break seed coats than wetter corn kernels. Kernel breakage will maximize
starch digestibility. In addition, wet corn forage chops more
consistently than drier corn forage. The chopper knives shred dry leaves
rather than cut, decreasing the uniformity of particle size and allowing
animals to sort further.
Corn silage contains up to 35% starch and needs to be supplemented
differently than most other Forages to High-producing cows due to this
high starch content. Excessive starch can lead to digestive upsets and
low energy intakes due to excess accumulation of fermentation acids in
the rumen. To optimally supplement forages, one must consider the starch
content and ruminal fermentability of grains as well as forages.
Low-starch forages such as alfalfa should be supplemented with a grain
such as high-moisture corn or barley, which will be highly fermented in
the rumen. This will increase the fermented organic matter in the rumen
and allow more efficient utilization of degraded forage protein.
Corn silage is high in starch which is usually highly digested in the
rumen. Therefore, supplementing corn silage with a starch source such as
high-moisture corn that is highly digestible in the rumen is likely to
cause digestive upset. To increase energy intake, corn silage should be
supplemented with a grain source that partially bypasses ruminal
fermentation yet has high whole-tract digestibility such as dried ground
corn. When corn silage is fed in combination with alfalfa, less bypass
starch is needed as the fraction of alfalfa is increased.
Feeding silage to beef cattle
Energy and protein provision represents the majority of the volume and
cost of beef rations. Corn silage may be a logical feed ingredient
alternative in providing adequate energy in beef cattle feeding
programs.
COW/CALF
The biological cycle of the beef animal results in tremendous diversity
in nutrient requirements, particularly energy, among the various classes
of beef cattle. The cycle begins with the cow/calf production phase
which includes both purebred and commercial production. Within this
production phase the nutrient requirements of the cow vary from very low
during the mid-gestation dry period to high requirements during early
lactation and rebreeding. As calves are weaned at approximately 7 months
of age, those entering the reproductive herd are fed at moderate energy
levels until near calving. The offspring intended for the slaughter
market are typically placed on high-energy, high-grain finishing
rations. Table 12 provides the energy requirements of beef cattle at
these various production stages with energy content of corn silage for
comparison. A ration management strategy that is often utilized to meet
the animal's energy requirement is to combine high-energy corn silage
with low-quality, low-cost roughages.
Table 12. Energy requirements of beef cattle.
|
Metabolizable energy |
Cattle type |
Mcal/day |
Mcal/lb |
Dry cow—mid-gestation |
|
.80 |
1000 lb |
14.5
|
.80 |
1400 lb |
18.7 |
|
Dry cow—late gestation |
|
|
1000 lb |
17.3 |
.88 |
1400 lb |
21.5 |
.86 |
Cows nursing calves—average milk |
|
|
1000 lb |
18.8 |
.93 |
1400 lb |
23.0 |
.90 |
Cows nursing calves—superior milk |
|
|
1000 lb |
22.7 |
1.10 |
1400 lb |
27.1 |
1.01 |
Two-year-old heifers nursing calves |
|
|
900 lb |
19.8 |
1.03
|
Replacement heifers |
|
|
750 lb, 1.4 lb daily gain |
16.4 |
.98
|
Steer Calves, medium frame, 600 lb |
|
|
1.5 lb daily gain |
15.3 |
1.04 |
3.0 lb daily gain |
18.8 |
1.39 |
Corn silage |
|
|
Few ears |
--- |
1.02 |
Well eared |
--- |
1.15 |
Cow/calf production in North America typically follows an annual cycle
of calving in the spring and weaning the calf crop the following fall.
Cows are sustained from calving to weaning on grazable forages,
predominantly grass pastures. Following weaning, cows are in
midgestation and their energy requirements can be met through the fall
and early winter with low-quality roughages such as crop residues.
Subsequently, nutrient requirements increase as cows enter late
gestation followed by lactation and rebreeding. This period is the
logical time for corn silage feeding as energy requirements
are high and the cows are often in confinement or can otherwise be "bunk
fed." Corn silage can be added into rations at this time to obtain
suitable cow body condition. Management of body condition via dietary
energy levels during late gestation through breeding season is important
for successful lactation and rebreeding. Cow body condition management
has become especially important in recent
decades as the beef industry has incorporated larger, European
continental breed into herds. These cows require greater levels of
metabolizable energy (table 12), which often cannot be provided by
conventional wintering forages.
GROWING AND FINISHING RATIONS
Corn silage makes an excellent feed for growing cattle following
weaning. Rations are often formulated with sufficient energy to allow
1.5 to 2.0 pounds of daily gain. Typical rations may contain 60% corn
silage with 30 to 35% hay and 5 to 10% supplement. Addition of grain to
corn silage-based rations such as this may reduce fiber digestibility
due to sustained lower ruminal pH. Because corn silage is fine chopped
and moist, an insufficient amount of saliva may be mixed with the
consumed ration. Feeding coarse-chopped or long hay with corn silage
will encourage rumination and saliva production for a more healthy
ruminal environment.
Corn silage is also routinely included in beef finishing rations. These
rations require only a minimum level of forage to provide ruminal
stability. Corn silage is an excellent forage for finishing rations as
it is finely chopped and has a high moisture content, making it very
mixable with other ration ingredients. Energy is widely considered the
limiting nutrient in finishing rations, therefore energy provided by
corn silage is of principal importance. The high level of grain in
finishing rations results in a very poor ruminal environment for fiber
fermentation. The stover fraction of corn silage therefore is probably
very poorly digested when fed in finishing rations. Consequently, the
grain content of corn silage is an important factor in the nutritive
value of silage for finishing rations.
IMPORTANT COMPOSITION CONSIDERATIONS
Energy values of corn silage fed in forage-based rations appear to be
reasonably well predicted by fiber (NDF and ADF) content. Research has
demonstrated a wide range of differences in fiber content of corn
silage. These differences are a function of grain content and of the
fiber concentration in the stover fraction. Differences in corn silage
fiber content affect differences in digestibility.
Since many beef cattle operators are more accustomed to feeding dry
feeds, the dry matter content of silage is often overlooked. Subtle
changes in the dry matter content will drastically change the as-fed
amounts of silage to be fed. Similarly, changes in dry matter content
should be reconciled by changes in the purchase price of the silage if
the beef producer is buying the silage. Producers should be aware of
changes in dry matter content and implement formulation and price
changes accordingly.
MYCOTOXINS IN CORN SILAGE
Mycotoxins are toxic substances produced by molds growing on grain or
feed. Mycotoxins can cause illness or death to livestock and humans.
While the vast majority of molds that can grow on silage are harmless, a
few species produce mycotoxins. The primary mycotoxins found in corn
silage are aflatoxin, deoxynivalenol (DON or vomitoxin), zearalenone,
T-2 toxin, fumonisin, and ochratoxin. Mycotoxin-contaminated silage fed
to cattle is rarely fatal. More commonly, contaminated feed reduces
growth rate, lowers feed conversion and reproductive rate, impairs
resistance to infectious diseases, and reduces vaccination efficacy.
TOXIC LEVELS
Establishing the toxic level for specific mycotoxins in cattle is
difficult and only limited data exists. Various classes of livestock are
more susceptible than others. Cattle are generally more tolerant than
other livestock species. Mycotoxin-contaminated feed poses a greater
health risk to young or pregnant animals and animals that are stressed.
The only regulated toxic feeding level for a specific mycotoxin is for
aflatoxin. The maximum dietary level for aflatoxin has been set by the
Food and Drug Administration (FDA) for cattle to be no more than 200
parts per billion (Ppb) for breeding cattle, 300 ppb for finishing
cattle, 20 ppb in feeds for lactating dairy cattle. Never use
contaminated feeds that exceed these levels.
The toxic levels for the other primary mycotoxins found in silage are
much less defined and significant controversy exists among researchers
working in this area. This controversy largely stems from the methods
used to determine the toxic effect. The toxic effect of a mycotoxin can
be defined in either acute or subacute (chronic) terms. The acute level
is the level that will produce a clinical (pathological) illness when
the animal is given a single dose over a relatively short period of
time. While the subacute or chronic effects have generally been
established through field observations of animals receiving contaminated
feedstuffs over longer periods of time. The subacute toxic level for a
particular mycotoxin is difficult to establish since some mycotoxins are
partially degraded by rumen microorganisms. Feeding practices that
influence rumen fermentation, such as frequency of feeding, diet
composition, level of intake, and duration of feeding, may have an
impact on the tolerance level of the animal. Likewise, most cases of
mycotoxin contamination involve more than one source of mycotoxin. It
has also been suggested that there are associative effects when multiple
sources of mycotoxin are fed. Thus, clinical studies which have
established the acute toxic level of a purified mycotoxin may actually
underestimate the toxic level found in contaminated feedstuffs fed in
field situations.
The guidelines in table 13 offer some practical recommendations for
establishing the tolerable levels of specific mycotoxins when fed to
cattle. The acute levels given are those established by clinical studies
which have clearly demonstrated a toxic effect. The subacute (chronic)
levels indicate the mycotoxin level in the diet which may reduce
performance.
Table 13. Descriptions of mycotoxins and illness symptoms for
cattle.
Mycotoxin |
Mold |
Acute level |
Subacute level
|
Illness symptoms |
Aflatoxin |
Aspergillus |
20 ppm (lactating dairy cattle)
200 ppb (breeding cattle)
300 ppb (finishing cattle) |
Reduced growth and milk production.
Increased susceptibility and reduced
immunity.
Liver damage and increased death losses.
Milk residues. |
Deoxynivalenol (DON or vomitoxin) |
Fusarium |
10 ppm |
500 ppb |
Reduced feed intake and lowered production.
Toxicity may increase when other mycotoxins
are present. |
Fumonisin |
Fusarium |
95 ppm |
?? |
Not known. |
Ochratoxin |
Penicillium and Apsergillus |
5 ppm |
1 ppm |
Diarrhea, kidney damage and reduced
production. |
T-2 |
Fusarium |
50 ppm |
100 ppm |
Intestinal hemorrhages, decreased food
intake, unthriftiness, and death. |
Zearalenone |
Fusarium |
500 ppm |
500 ppb |
Decreased fertility, swelling around
the vulva, and irregular and prolonged estrus cycles (estrogen). |
Total dietary concentration
Ppm = parts per million or mg/kg; ppb = parts per billion or µg/kg. |
INCIDENCE OF MYCOTOXINS
It is suggested that the incidence of certain mycotoxins are related to
geographical location. Mycotoxins produced by Aspergillus, such as
aflatoxin, are more prevalent in the southern United States.
Mycotoxins produced by Fusarium, such as DON, T-2, and Zearalenone, may
be more prevalent in the northern United States and are associated with
cool, moist conditions and diseases such as ear or stalk rot in corn.
However, aflatoxin contamination has been reported in corn silage in
Wisconsin and other northern states and Fusarium mycotoxins have been
reported in North Carolina and other southern states.
Since molds are spore-forming organisms, they have the unique ability to
survive even the most unfavorable growth conditions. They will grow
wherever there is a suitable substrate, pH, and adequate amounts of
water, oxygen and heat. Mold growth and potential mycotoxin production
can occur on the growing corn plant, during the initial aerobic phase of
the ensiling process, on the exposed surfaces of the silo during storage
and feedout, and in the bunk once fed.
Certain agronomic practices are associated with higher incidences of
mycotoxin-producing fungi. No-till or minimum till cultivation, corn on
corn cropping patterns, delayed planting, heavy applications of manure,
and fertility imbalances have all been implicated. Likewise, corn plants
subjected to insect, wind, or hail damage are more prone to mold growth
and potential mycotoxin contamination.
MYCOTOXIN TESTING
Analytical techniques for mycotoxin testing have improved over the past
decade. Several commercial laboratories are available and many state
universities have diagnostic laboratories which provide screens for a
large array of mycotoxins. Cost of analysis has been a constraint, but
can be insignificant compared with the economic consequences of
production and health losses related to mycotoxin
contamination.
As with any analytical analysis, the results are only as valid as the
sample is representative. Since molds can produce very large amounts of
mycotoxin in small non-uniform locations, representative sampling is
critical. Samples should be delivered to the lab as quickly as possible
since mycotoxins can form in the collected sample if allowed to heat or
if exposed to oxygen. Acceptable levels of mycotoxin should be
conservatively low due to non-uniform distribution, uncertainties in
sampling and analysis, and the potential for more than one source in the
diet.
PREVENTION AND TREATMENT
Prevention is the most cost-effective and safest way to avoid problems
associated with mycotoxins. Since mold contamination begins with the
growing plant, sound agronomic practices which minimize the incidence of
insect and disease levels will reduce the potential contamination in the
silage. Often environmental factors out of the producer's control such
as wind and hail damage, drought, or early frost, will dictate the use
of the crop for silage. Under these conditions, the mold level on plants
will be elevated and this increases the potential risk for mycotoxin
production.
The key to the prevention of mold growth during the ensiling process is
the elimination of air as quickly as possible, and managing the silo to
minimize air infiltration into the ensiled mass during storage and
feedout. Employing sound silage management practices including rapid
filling, harvesting at the correct moisture level, adequate compaction,
covering exposed surfaces, and rapid feedout will go a long way in
minimizing mold growth and potential mycotoxin contamination in silages.
The use of some silage additives may be beneficial in reducing the risk
of potential mycotoxin production if they are shown to reduce mold
growth. Ammonia and/or propionic acid appear effective in this regard.
Certain bacterial inoculants may also be beneficial since they have been
shown to increase the rate of pH decline in the silage and extend
aerobic stability of the silage on feedout.
At present there is no practical way to detoxify mycotoxin-contaminated
silages. If unacceptably high levels of mycotoxins occur, dilute or
eliminate the silage from the diet. The addition of absorbent materials,
such as clays (bentonites) or anticaking agents (hydrated sodium calcium
aluminosilicate), to contaminated rations has helped in some cases and
may warrant consideration. Avoid feeding moldy clumps of silage or
visibly moldy silage, particularly to pregnant animals or young stock.
Further Reading
Wisconsin
Note: Web resources for Wisconsin are maintained by
Mike Rankin and
Team
Forage. Please see
http://www.uwex.edu/ces/crops/uwforage/Silage.htm
for an up-to-date listing.
Impact
of Feed Prices on Cost of Simulated Average and High Corn Silage Rations
by Paul Dyk, Fond du Lac County Dairy and Livestock Agent, and Dr. Randy Shaver,
UW Extension Dairy Scientist
Degree of Starch
Access (DSA): Starch Digestion in Forages and Grains Fed to Dairy Cattle
by Pat Hoffman and Randy Shaver, UW Extension Dairy Scientists, A "Focus on
Forage" Fact Sheet.
Milk2006
for Corn Silage
This spreadsheet, developed by Dr. Randy Shaver, Dr. Joe Lauer, Dr. Jim Coors, and
Pat Hoffman, is the latest version of the "MILK" series spreadsheets.
It more accurately estimates the feeding value of corn silage than past versions.
Crop Processing
and Chop Length of Corn Silage: Effects on Intake, Digestion, and Milk Production
by Dairy Cows
by Dr. Randy Shaver, UW Extension Dairy Scientist, et al.
Influence of Mechanical
Processing on Utilization of Corn Silage by Lactating Dairy Cows
by Dr. Randy Shaver, UW Extension Dairy Scientist, et al.
Processing and Chop
Length Effects in Brown-Midrib Corn Silage on Intake, Digestion, and Milk Production
by Dairy Cows
by Dr. Randy Shaver, UW Extension Dairy Scientist, et al.
Stage of
maturity, processing, and hybrid effects on ruminal in situ disappearance of whole-plant
corn silage
Corn Silage Hybrid
Effects on Intake, Digestion, and Milk Production by Dairy Cows
by Dr. Randy Shaver, UW Extension Dairy Scientist, et al.
Impacts of
2004 Growing Season on Silage Quality
A presentation given by Joe Lauer, UW Extension Corn Agronomist, at the 2005 Wisconsin
Fertilizer, Ag Lime, and Pest Management Conference
Can we manage corn silage stover
quality?
by Dr. Joe Lauer, UWEX Agronomy Advice, December, 2003
Dairy Cattle
Feeding Tips for Drought Stressed Corn
by Dr. Randy Shaver and Pat Hoffman, UW Extension Dairy Scientists
The Effect of Maturity
on NDF Digestibility
by Pat Hoffman, UW Extension Dairy Scientist, Marshfield Ag Research Station, et
al. A "Focus on Forage" Fact Sheet.
Agronomic Considerations
for Molds and Mycotoxins in Corn Silage
by Mike Rankin, Crops and Soils Agent, UW-Extension-Fond du Lac County and Craig
Grau, Extension Plant Pathologist - UW Madison. A "Focus on Forage"
fact sheet. For full length, referenced paper:
click here
Understanding NDF Digestibility
of Forages
by Pat Hoffman, UW Extension Dairy Scientist, Marshfield Ag Research Station,
et al. A "Focus on Forage" Fact Sheet.
Enhanced Forage Evaluation:
NDF Digestibility
by Scott Reuss, Marinette Co. Agricultural Agent
Interpretation and
Use of Silage Fermentation Analysis Reports
by Limin Kung, University of Delaware, and Randy Shaver, UW Extension Dairy
Scientist. A "Focus on Forage" fact sheet.
Estimating Silage
Energy and Milk Yield to Rank Corn Hybrids
by Dr. Randy Shaver, UW Extension Dairy Scientist et al.
Feed Delivery
and Bunk Management Aspects of Laminitis
by Dr. Randy Shaver, UW Extension Dairy Scientist
Supplementation
of High Corn Silage Diets for Dairy Cows
by Dr. Randy Shaver, UW Extension Dairy Scientist
Influence of Corn
Silage Particle Length on the Performance of Lactating Dairy Cows Fed Supplemental
Tallow
by Dr. Randy Shaver, UW Extension Dairy Scientist, et al.
Impact of the Maturity
of Corn for Use as Silage in the Diets of Dairy Cows on Intake, Digestion, and Milk
Production
by Dr. Randy Shaver, UW Extension Dairy Scientist, et al.
Adding
Enzymes to Silage
by Pat Hoffman, UW Extension Dairy Scientist, Marshfield Ag Research Station and
Richard Muck, USDA Dairy Forage Research Center. A "Focus on Forage"
fact sheet.
Adding Urea to Corn Silage
by Pat Hoffman, UW Extension Dairy Scientist, Marshfield Ag Research Station.
A "Focus on Forage" fact sheet.
Corn Silage
Harvest Management
by Dr. Randy Shaver, UW Extension Dairy Scientist, Dr. Joe Lauer, UW Extension Agronomist
and Dr. Kevin Shinners, UW Ag Engineer
Balancing Use of Corn Silage
and Alfalfa in Dairy Rations
by Dr. Randy Shaver, UW Extension Dairy Scientist
FeedVal
This spreadsheet, developed by Drs. Terry Howard and Randy Shaver, is a program
to compare values of different feed sources - Calculated from Crude Protein,
TDN, Ca, and P (Referee Feeds Used to Calculate Value of Nutrients).
FeedVal4
This spreadsheet, developed by Drs. Terry Howard and Randy Shaver, is a program
to compare values of different feed sources - Feed Comparative Values Calculated
from Protein (UIP), TDN, Fat, Calcium, & Phosphorus.
Pricer
This spreadsheet, developed by Drs. Terry Howard and Randy Shaver, is a program
to calculate MAXIMUM price for forage based on a base forage.