Advances in Inoculants For Silage
Director of Technical
Services
Chr. Hansen BioSystems
Limin Kung, Jr., Ph.D.
Department of Animal and
Food Sciences
The making of silages is a necessary evil. In order to manage feed inventories we must ferment wet feeds to keep them from spoiling over the course of the feedout period. Unfortunately, fermentation is a relatively uncontrolled process, which can result in rather substantial dry matter losses. (Table 1) The goal in the development of silage additives, and especially bacterial inoculants, is to control fermentation to ensure a consistent quality feed, minimize dry matter losses and in many cases improve animal intake and performance.
The silo should be filled with material that is cut
at optimum maturity, moisture, and chop length, to ensure good fermentation and
high quality forage. Proper maturity is
important to make sure the maximum amounts of nutrients are available to the
animal during feedout.
Proper maturity assures adequate fermentable sugars
for silage bacteria and maximum nutritional value for livestock. Maturity also has a tremendous impact on
moisture with unwilted forage crops such as corn silage. Variation in fiber digestibility can vary
from 30-50% for traditional forages such as alfalfa and corn silage, and can
affect the energy content of the ration, microbial production, and laboratory
prediction of energy content. Ruminal
fermentation of starch varies from less than 50% to over 90% for grains,
depending upon plant source, plant maturity, and processing. Variation in rumen fermentable starch can
affect rumen pH, dry matter intake and microbial protein production (Mahanna,
1997).
Proper moisture is necessary to ensure optimum
packing and removal of oxygen. With most
crops, 63-68% moisture is optimum.
Material can be ensiled at less than 60% moisture, but increased packing
time will be necessary to remove oxygen.
Avoid moisture greater than 70% with alfalfa haylage if possible. Ensiling alfalfa at high moisture
significantly increases the risk of poor quality fermentation. Clostridial organisms proliferate at high
moisture and produce butyric acid. These
organisms also seriously degrade protein and produce compounds and silage
unacceptable for high producing cows.
The best way to avoid this type of fermentation is to field wilt alfalfa
to less than 70% moisture.
Theoretical Length of Cut
Whole plant corn silage should be chopped at 3/8 –
1/2 inch TLC. Longer chop can create
difficulties in packing and unloading. It also results in kernels passing into
the manure and preferential sorting by cows at the bunk. Recently, however, many producers are using
kernel processors on corn silage. With
the use of these devices, corn silage can be effectively chopped at 3/4 inch
TLC and still be adequately packed in bunker silos.
Haylage should be chopped at 3/8 inch TLC to provide
more than 15-20% of forage particles at greater than 1 1/2 inches long. Chopping haylage at greater lengths to
improve effective fiber in the diet is a common practice currently employed by
many producers. Haylage tends to
stratify in bunkers and longer chop makes it more difficult to unload. Digging out long cut haylage allows for
deeper air penetration into the silage mass, which can lead to poor aerobic
stability and higher dry matter losses.
A reasonable compromise may be to shorten the TLC in haylage and use
longer cut processed corn silage for effective fiber in the diet.
It has been shown that acid detergent fiber (ADF) is
as much as four percentage units higher in coarse cut haylage compared to fine
cut haylage. The higher ADF results in a
lower predicted energy density. It would
take the addition of more than 460 bushels of corn for each 1000 tons of
haylage to give coarse cut material the same energy density as finer cut
material (Ruppel et al., 1995).
FILLING AND PACKING THE SILO
The silo should be filled as quickly as possible
within the limitations of harvest and packing equipment. Adequate packing is one of the most critical
operations in the filling of a bunker silo.
Insufficient packing allows oxygen to be trapped, which can increase dry
matter loss due to extended plant respiration.
Poor pack subsequently allows more oxygen penetration into the silage
mass when feedout begins, which also leads to decreased aerobic stability. The operator must match the packing effort to
filling speed. Packing at a minimum rate
of 800 to 1000 hour-pounds/ton has been shown to result in better aerobic
stability (Ruppel et al., 1995). Use the
following formulas (Ruppel, 1997) to determine filling rate:
Filling Rate (tons per hour)
= Packing Vehicle(s) Weight ÷ 800
To calculate the additional packing weight needed
for fast filling days, use the following formula:
Packing Vehicle(s) Weight =
Filling Rate (tons per hour) x 800
More tractors, heavier tractors, wheeled dozers, and
enlarged blades or plows are being used to increase packing capacity on many
farms today (Ruppel, 1997). Packing
technique is also important. Spreading
out incoming loads as soon as possible and attempting to have less than 6
inches of silage under the packing wheels helps transfer the weight of tractors
into silage compression. This ensures
rapid and complete removal of oxygen.
Packing is important, but use caution when packing
very wet immature crops, especially alfalfa haylage. Over-packing of this material can squeeze
water from tender plant cells and rupture them.
This water can create effluent, which robs the silage of valuable
soluble nutrients. Over-packing can also
allow water to collect along the different strata of the silage mass, creating
streaks of very wet silage. If the
moisture is greater than 70% in these streaks, clostridial fermentation may be
initiated, which can dramatically reduce the quality of silage in these
areas. When packing this type of
material, 800 hour-pounds/ton should be sufficient (Kautz, 1997).
Filling method is also important in maximizing dry
matter recovery and energy content.
Packing fresh cut forage into bunkers at a 30 degree angle is known as a
progressive wedge and is the most efficient way to fill a bunker. Horizontal layering of forage or dumping off
the load at nearly full height results in higher ADF and lower non-structural
carbohydrate levels in the ensiled material (Ruppel, 1997).
Keeping the fresh forage in a slightly concave
configuration can also increase packing efficiency. Maintaining the material in
this shape until the top of the wall is reached will help direct the weight of
the packing vehicle toward the outside walls of the silo. This can result in better packing density and
less shrink along the walls.
One other important point to
remember when sizing, filling and packing silos is to build the structure big
enough so that silage does not go above the tops of the walls. Rounding off the material just at the top of
the wall to about 2 – 4 feet above the wall in the center provides an adequate
slope for rain to run off, but still allows safe and efficient packing.
The final step in managing a bunker silo is to cover
the silage mass to prevent exposure to oxygen, sunlight, rain and snow during
storage. The value of covering is often
discussed, but the data conclusively shows the value of a cover. Many ideas have surfaced as to what cover is
best. Currently 4 – 6 mil black or
black/white sandwich plastic is the best option. This plastic should be secured with tires
(preferably split) placed edge to edge on top of the plastic.
Research data has shown that silage (either haylage
or corn silage) will lose an AVERAGE of 30% of its dry matter in the top 3 feet
when stored in an uncovered bunker silo.
Most of the losses are highly valuable nutrients such as non-structural
carbohydrates and soluble protein. This
would put the value of the material lost at about $100 per ton of dry
matter! Leaving a bunker silo uncovered
is equivalent to using 30% of the top three feet of silage as your silo cover,
and this can be incredibly expensive.
Using silage as a cover is nearly 20 times more costly than even the
more expensive plastic silo cover.
The cover on a bunker silo, in
addition to being topped with tires, can further be secured at the edges with
sandbags. Experience has shown that
folding the plastic back on itself (about 18 inches of overlap) and then laying
sandbags next to the edge of the wall helps keep moisture from running down the
outside edge of the silage mass. Do not
place the sandbags on the top of the wall.
This will lead to increased spoilage as the silage shrinks away from the
cover (Kautz, 1997). Bunker covers that
are not adequately secured may be worse than no cover at all. A flapping bunker cover acts as a conduit to
pump more air along the surface of the ensiled material and can increase the
depth of the top spoilage.
ENSILING
FORAGES
If all the management practices are
carefully followed, excellent quality silage can be made with a minimum of
loss. If the silage is made properly, it
can be stored for long periods as long as exposure to oxygen is minimized.
There are several phases recognized
in silage fermentation. The first phase
is sometimes referred to as the “aerobic” phase because it is characterized by
the presence of oxygen. No matter how
good management is during silo filling, some oxygen will be trapped in the
silage mass. Depending upon how much air
is trapped, this phase can continue for several hours or even several
days. Until all the oxygen is gone,
aerobic bacteria and yeast can grow and negatively affect dry matter
recovery. Plants also continue to
respire until the oxygen is gone, which will also negatively affect dry matter
recovery and protein quality.
When anaerobic conditions (no
oxygen) have been established, fermentation organisms dominate the silage
mass. During this phase, lactic acid
bacteria usually dominate and produce lactic acid from available water soluble
carbohydrates (sugars). How well this
phase proceeds depends on the numbers and types of organisms present in the
silo.
The next phase of fermentation is
often referred as the “stable” phase.
This phase occurs when the pH has reached its low point and the silage
is kept free of oxygen. Silage can be
kept under these conditions for substantial periods of time.
The final phase is the “feedout
phase”. This phase occurs when the
silage is re-exposed to oxygen on the face, in the mixer, and in the
feedbunk. During this phase, spoilage organisms
present in the silage mass can begin to grow.
These organisms (primarily yeasts and some molds) produce heat and cause
substantial additional dry matter losses if the feedout of the silage is not
carefully managed.
SILAGE
INOCULANTS
Organisms
The addition of specially selected
lactic acid producing bacteria (LAB) to silage is designed to dominate the
fermentation and produce a high quality silage.
Some common LAB used in silage inoculants include Lactobacillus
plantarum, Pediococcus acidilactici, Pediococcus pentocaceous and Enterococcus
faecium. Microbial inoculants may be
single or multiple strains of bacteria selected for their ability to dominate
the fermentation. Interactions among
strains can enhance effectiveness and this is the reason for multiple strain
products.
Fermentation
and Animal Responses
Alfalfa, grass and cereal grain
crops have responded well to bacterial inoculation. The fermentation of high moisture corn has
also been improved with inoculants. LAB
inoculation of corn silage has resulted in less consistent results. Bolsen et al. (1992)
reported that in 19 studies conducted at
When compared to untreated silages,
silages treated with LAB have been shown to have lower pH, acetic acid, butyric
acid and ammonia-N, but higher lactic acid content. Muck and Kung (1997) showed that this
occurred in 60 percent of studies reviewed.
Dry matter recovery and dry matter digestibility were improved in
approximately 33 percent of studies.
Bunk life (aerobic stability) was improved in only 33% of studies and in
fact inoculation with LAB has, in many instances, made aerobic stability
worse. This is most likely due to lower
levels of acetate and other fungal end products. Yeasts typically initiate
aerobic instability in corn silage and high moisture corn. Recent studies (Leedle et al., unpublished
data) suggest that LAB can be selected to improve bunklife in corn silage. This work demonstrated that bunklife could be
significantly increased (average of 28 hours) when inoculating with LAB
selected to inhibit five of the more common spoilage yeasts found in corn
silage.
Inoculation
Rate, Use and Storage
The organisms in bacterial
inoculants must be present in sufficient numbers to effectively dominate and
direct the fermentation. Most research
has shown that the optimum inoculation rate for L. plantarum based inoculants
is 100,000 colony forming units per gram of wet forage.
Limited data suggests that doubling or tripling this to
200,000-300,000 may increase the effectiveness of the inoculant. Additions of 1,000,000 cfu per gram are not
likely to be cost effective in
Most inoculants are available in a
water soluble or granular form.
Inoculants applied in the granular form are often mixed with limestone
or other flowable carriers. Inoculants
to be applied as a liquid come as dry powders and are mixed with water just
prior to use. Use of chlorinated water
may kill the inoculant organisms if levels of chlorine are greater than 1.5-2.0
parts per million.
Microbial inoculants can be applied
to the forage at a variety of locations.
Application at the chopper is highly recommended in order to maximize
the time that the bacteria have in contact with fermentable substrates. This is more important if silage is being
stored in a bunker or open stack because it is difficult to achieve good
distribution onto silage from a forage wagon.
Distribution of the inoculant is less of a problem if it is applied at
the blower of a tower silo or at the bagger.
Inoculants can be applied in a liquid or granular form. Data (Whiter et al, 1999) suggests that on
higher dry matter silages (>45%), using a water soluble inoculant is
preferable since low moistures in these silages limits fermentation. Water soluble inoculants may be more
effective since the bacteria are re-hydrated when they are put on the silage
and consequently will grow faster.
Bacterial inoculants must be alive
when applied to the silage. Most
reputable products are freeze dried, moisture controlled, mixed with a dry
inert carrier and stored in a foil lined heat sealed bag. Beware of products in paper stitched
bags. These bags cannot keep moisture
out and the life span of the inoculant organisms is greatly reduced. Moisture, oxygen and sunlight are the three
things that will destroy these organisms the quickest. Use common sense and store the material in a
cool, dry environment. Open bags should
be used during the current season and not carried over. Once mixed, water soluble products should be
used within 48-72 hours.
Miscellaneous
Organisms
Several bacteria that are not LAB
have been tried as silage inoculants, specifically for the purpose of improving
aerobic stability. For example,
Propionobacteria are able to convert lactic acid and glucose to acetic and
propionic acids that are more inhibitory to molds than is lactic acid. Florez-Galaraza et al., (1985) reported that
addition of Propionobacteria shermanii prevented growth of molds and greatly
reduced the initial population of yeast in high moisture corn where the final
pH was greater than 4.5.
Lactobacillus buchneri, a
heterolactic bacteria capable of producing lactic and acetic acid, has been
studied for its potential ability to improve aerobic stability of silages. In
Buffered
Propionic Acid-Based Additives
Propionic acid is effective in
reducing yeasts and molds which are responsible for aerobic deterioration in
corn silage and high moisture corn. The
antimycotic effect of propionic acid is enhanced as pH declines. Historically, aerobic stability was improved
when large amounts of propionic acid (1-2% of silage DM) were added to silage,
but the high percentage of acid restricted fermentation. Propionic acid is also difficult to handle
because it is very corrosive. Hence, the
acid salts have been used in some commercial products. The efficacy of propionic acid and its salts
is closely related to their solubility in water. Of these salts, ammonium propionate is the
most soluble in water at 90%. Other
forms are much less soluble. Recent
additives containing buffered propionic acid and other antifungal components
(i.e. citric acid, benzoic acid, sorbic acid) have been applied at much lower
rates than the acid itself (2-4 pounds per ton of fresh forage weight). These low application rates usually do not
affect silage fermentation, but do reduce the numbers of yeasts that cause
aerobic spoilage. Several products
containing buffered propionic acid were designed for application onto silages
or total mixed rations just prior to feeding to prevent heating and spoilage in
the feed bunk. Research from Kung et
al., suggests that controlling yeasts at the time of ensiling is more efficient
than trying to control their numbers and metabolism in the feedbunk.
CONCLUSION
Silage inoculants and buffered
propionic acid-based additives can be useful tools to improve silage quality
and animal performance, but management practices must come first. Only producers who follow the best management
practices as outlined here will see a response from a good silage additive.
How should a silage additive be
evaluated? Although inoculants do change
the fermentation pattern of silages, such changes alone are not a compelling
reason to use a specific inoculant.
Three things should be considered when choosing an inoculant. Look for a broad and extensive data base that
proves efficacy under a wide range of conditions. Look for products that support and increase
milk yield or milk composition, also support improvements in dry matter and/or
nutrient recovery and also support improvement in aerobic stability. Finally, choose an inoculant from a reputable
company that stands behind their products and offers excellent technical
service support.
|
Table 1. Average (and
typical range) of DM losses associated with ensiling systems |
||||||
|
Storage Type |
Trench Stack |
Horizontal Bunker |
|
O2 |
Bag |
Round Bale |
|
% DFM |
35 |
35 |
35 |
55 |
35 |
35 |
|
Loss Type |
|
|
% DM Losses |
|
|
|
|
Respiration |
4 |
4 |
4 |
6 |
4 |
4 |
|
Harvesting |
2 |
2 |
2 |
3 |
2 |
4 |
|
Storage |
15 |
12(10-15) |
9(8-9) |
5 |
7(5-9) |
18(10-25) |
|
Feedout |
4 |
4 |
2 |
2 |
4 |
4 |
|
TOTAL |
25 |
22 |
17 |
17 |
17 |
30 |
|
|
|
|
|
|
|
|
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