Ag-Bag MB7010HyPac - Manual (Page 119)

4
T
HE
3M’
S OF
S
ILAGE
Appendix B
Ag-Bag International, Ltd.
MB7010 HyPac November 2003
such as acetic and butyric acids later used by
lactobacilli and streptococci to produce lactic acid.
Photolytic enzymes from the plant are also active
in this phase, and they break down some of the
plant proteins into amino acids. This phase of
respiration is complete when the oxygen in the
mass is completely depleted, and the action of the
anaerobic microorganisms begin. Aerobic
respiration lasts from 5 to 10 hours under good
storage conditions.
T
HE
F
ERMENTATION
S
TARTS
Phase 1 – This is a relatively short phase
characterized by the beginning of anaerobic
microorganism activity. The cell contents diffuse
out of the cell due to the chopping of the plant, and
are used by bacteria clinging to the plant when
placed in the bag. The formation of acetic and
butyric acids are characteristic of this phase. The
life of organisms producing these acids is short
due to the drop in pH produced by their own activity.
Phase 2 – This phase is the initiation of the lactic
acid fermentation. This activity is well underway at
the end of three days and the establishment of this
activity completes Phase 2.
Phase 3 – Lactic acid production is continued in
this phase and reaches it’s peak which should be
3.0 - 13.0 percent of the dry matter and a pH that
is constant at about 4.0. No further changes occur,
and the silage is fermented if the pH remains
between 4.0 and 4.2 for corn silage, and 4.0 and
5.0 for other crops, and no air is allowed to enter
the mass.
Phase 4 – This is a stage of quiescence or
inactivity. The material has a pH of 4.0 - 4.5 and if
water and oxygen remain excluded, no further
chemical changes occur and the material will
remain in this preserved state almost indefinitely.
Phase 5 – This is an undesirable phase. If the pH
does not drop below approximately 4.2, or if air is
allowed to enter the silage, butyric acid production
is initiated, converting the soluble carbohydrates
and lactic previously formed to butyric acid which
is characteristic of spoiled silage. Also, proteins
are broken down to amino acids and these are
further degraded to other nitrogenous compounds,
which may lead to a reduction in a level of digestible
protein.
F
ERMENTATION AND
I
NOCULANTS
The general knowledge of the biochemistry and
microbiology of silage fermentation has increased
tremendously in the last 25 years. Silage is a
product of anaerobic fermentation. It involves the
conversion of water soluble carbohydrates
(sugars) to lactic acid, which drops the pH to a
level sufficient to inhibit any further biological activity
(change) in the ensiled material when maintained
under anaerobic conditions.
In most circumstances, good silage is achieved
by encouraging the dominance of lactic acid
bacteria (the good guys), and discouraging the
activity of clostridia and yeast ( the bad guys). In
the initial stages of ensiling, plant respiratory
enzymes (bad ones) oxidize soluble
carbohydrates, resulting in heat production and
decreased amount of sugars available for
fermentation.
P
RINCIPLES OF
E
NSILING
Aerobic phase. As crops are put into the bags,
two things start to happen: respiration and
proteolysis (enzyme action), which are attributed
to the activities of plant enzymes. Respiration is
the complete breakdown of a substance to carbon
dioxide and water, using oxygen. Harvesting of the
forage crushes and chops the plant, damaging the
cells and releasing many plant enzymes. Some of
the enzymes, amylase and hemicellulase, break
down starches, increasing the level of sugars in
the plant. Of these processes, respiration is most
detrimental to silage quality because:
1. Respiration causes a loss of dry matter.
2. The plant uses up existing plant sugars during
respiration. The loss of sugar is crucial at this point
as it affects preservation and nutritional value.
Sugars are the principal food for the lactic acid
bacteria that ferment the crop and a loss of sugar
also reduces the energy values.
3. Prolonged aerobic conditions allow yeasts and
molds to grow to high levels. Large populations of
these microorganisms can predispose the silage
to heating when the bag is opened for feed-out.