E-Z Sile - Silage Fermentation
MicroMaster/TB: EZS001
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This is a brief overview of the types of fermentation possible to take place in silage.
This knowledge sets the basis for a need to favorably direct or control fermentation
and to have a very rapid lactic acidification of ensiled forage and high moisture ground
and packed grain.
HOMOLACTIC FERMENTATION:
This can be achieved by over populating silage with a product containing homofermentative bacteria.
Homolactic is the most efficient type of fermentation and the maximum result would
be 100% dry matter recovery and 99.3% energy recovery. Most producers aim for high
dry matter recovery so efforts to insure Homolactic fermentation are highly desirable.
Homolactic fermentation will look like this:
Homolactic bacteria + glucose -----> 2 lactate
If Homolactic bacteria are not prevalent and lactic acid is not being produced rapidly,
then a less desirable type of fermentation will take over.
HETEROLACTIC FERMENTATION:
This type of fermentation is slower and less efficient in lactic acid production and also
produces some compounds that deteriorate dry matter in the process. Heterofermentation yields a greater energy concentration per unit of dry matter than the
forage state before it was ensiled. With this in mind, be aware that dry matter recovery
is not an indicator of energy recovery or vice versa. This less efficient type of
fermentation would look like this:
Heterolactic bacteria + glucose -----> lactate + ethanol + CO2
This fermentation reaction would result in 76% dry matter recovery and 98% energy
recovery. Ethanol is a source of energy converted from sugars and is a natural result
of fermentation. This is why recoverable energy is still good but in the form of ethanol
instead of starch converted sugar. Ethanol levels of less than .6% are considered to be
of no consequence to the silage quality. Levels above 1% should cause concern due to
undesirable Heterolactic, yeast or clostridial fermentation having taken place. Because
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lactic acid is produced at an insufficient and slower rate, clostridial fermentation may
take over in the process of ensiling.
CLOSTRIDIAL FERMENTATION:
This is the least desirable fermentation type and is generally considered destructive to
the forage mass. The destruction may increase the buffer capacity of the silage by
producing ammonia, carbon dioxide and free amino acids. With this condition, the
usual amounts of fermentable sugars to attain a pH of 4.0 are not adequate.
Therefore, pH will not be low enough to properly ensile.
Also in clostridial
fermentation, protein degradation is caused yielding acetic acid, ammonia and carbon
dioxide. To get an accurate determination of the effect ensiling has on protein; one
must pay attention to the analysis of ammonia nitrogen as a percent of total nitrogen.
This will reflect protein breakdown by the undesirable clostridial process. The higher
the ammonia nitrogen percentage, the less desirable the fermentation process was that
took place. Clostridial fermentation may look like this:
Clostridial bacteria + 2 lactate -----> butyric acid + 2CO2 + 2H2
This reaction would result in a dry matter recovery of 49% and an energy recovery of
82%. The loss of dry matter and energy along with other well known problems
associated with clostridial fermentation and the presence of butyric acid give solid
grounds for the insurance of proper Homolactic fermentation.
One can see, the clostridial fermentation degrades the desirable lactate state of the
forage using up what good the Homolactic bacteria may have done to that point. With
this in mind, the need for a rapid lactic acid formation by Homolactic fermentation is of
extreme importance.
There is a critical need for producers to understand their silage quality after ensiling,
related to the quality of the forage before it was ensiled.
It must be recognized that laboratory evaluation needs supplementary data for a
correct interpretation. Crops being ensiled vary considerably as do conditions under
which they are ensiled. Therefore, if proper evaluation of any silage or silage
treatment is to be done, it is important to have reference samples of the forage taken
at the time of ensiling.
Information about conditions such as temperature, humidity, time of day, percent
moisture, crop maturity and drought stress can be valuable when silage is taken out of
the silo later and analyzed.
In taking samples, air should be squeezed out of the sample bag as complete as
possible. The bags should be well sealed and frozen promptly. Note the general
location of the silo where the sample was taken and if the cutting is from a different
field, farm or variety of crop. These can be matched with samples taken later from the
ensiled crop for lab analysis and comparative evaluation made to determine relative
feed values.
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Let's look at some things to evaluate in the silage analysis report.
pH:
This value is important but does not tell everything we want to know. Certainly to
lower the pH to 4.0 is desirable but when samples are taken from the silo days or
weeks later, a low pH tells us only that fermentation has taken place, not the
quality or type of fermentation that has occurred.
For example, Heterofermentation will lower pH as will clostridial fermentation, however, both of these
types are considered undesirable.
Lactic acid and volatile fatty acids:
The amount of lactic acid being formed is extremely important because its
quantitative relationship to acetic acid and butyric acid reflect the speed of
production that has occurred. Researchers have concluded that the ideal,
desirable fermentation should have a 3:1 ratio of lactic acid to acetic acid and a
very low level of butyric acid. These values should fall into these approximate
relative amounts:
Lactic acid %
Acetic acid %
Butyric acid %
1.5-2.5
.5-.8
below .1
Remember, silage with pH of 4.2 or below with an acid profile in the range and
relationship stated above indicates a well fermented silage provided it was
acidified rapidly.
AMMONIA NITROGEN AS PERCENT OF TOTAL NITROGEN:
This is another important indicator of fermentation quality. A "rule of thumb" is that
ammonia nitrogen should not be greater than 5-8% of the total nitrogen in the silage.
When it is greater than this, an undesirable protein breakdown has occurred. This
breakdown is usually caused by clostridial fermentation and exhibits large losses of dry
matter and energy as well.
DRY MATTER RECOVERY PERCENT:
This is often a good indicator of proper Homolactic fermentation if the loss of dry
matter is very small. Heterolactic and clostridial fermentations are at least partially
characterized by more substantial dry matter losses.
As for proper analysis of volatile products in silage such as total nitrogen, non-protein
nitrogen, ammonia nitrogen, volatile acids (acetic, propionic, butyric) and caloric value
determinations should be determined on a wet basis. Fiber, lignin and mineral
components can be made on a dried residue.
Acid detergent fiber nitrogen (ADFN), insoluble acid and carotene values can be
indicative in heat damage determination. High temperature is very typical of improper
fermentation.