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Forage Fermentation Profiles
By Dr. David P. Casper, P.A.S., Dairy Nutritionist
The measurement of the fermentation profile
of forages is another diagnostic tool to evaluate the
performance characteristics of forages when fed to dairy
cattle. A fermentation profile consists of measuring
the pH and volatile fatty acid (lactic, acetic, and
butyric acids) concentrations of ensiled forages. Agri-King
has extensively used these assays in the development
of Silo King. However, these assays have also been used
in special situations by the Nutrition Department to
evaluate performance and herd health problems when fermented
forages are fed. This is why fermentation profiles have
been gaining in popularity with both Agri-King's Area
Managers and the Dairy Industry.
What information can a forage fermentation
profile provide? To help answer this question, the fermentation
profiles of 1483 haylage and 1348 corn silage samples
were summarized and the results are presented in Table
1 and Figures 1 through 4. Caution must be used in evaluating
these averages because the data set contains both excellent
and poorly fermented forage samples. Therefore, Table
1 also contains the recommended guidelines for an ideal
fermentation profile. While the averages for haylage
and corn silage given in Table 1 are close to the recommended
guidelines, a large range in the values was observed.
Forages with fermentation profiles outside of the recommended
guidelines can lead to performance problems in dairy
cows.
| TABLE 1 |
| No. samples |
1483 |
1348 |
| ITEM |
HAYLAGE |
CORN SILAGE |
RECOMMENDED |
| Moisture, % |
59.9 |
66.7 |
65 - 70 |
| pH |
4.9 |
4.0 |
<4.5 |
| Lactic Acid, % |
4.5 |
4.5 |
>4.0 |
| Acetic Acid, % |
2.1 |
2.0 |
<2.0 |
| Butyric Acid, % |
0.3 |
0.04 |
0.0 |
The greatest factor responsible for forages
having a fermentation profile not achieving the recommended
guidelines was moisture. The rate of decline and extent
of the final pH of an ensiled forage depends on moisture.
Harvesting forages at recommended moisture levels is
crucial to achieving optimal fermentation profiles.
Harvest moisture is mainly controlled by farm management
and environmental factors. Figures 1 and 2 show that
the lowest pH occurred in haylage at 60-65% moisture
and 67-70% moisture for corn silage.
Forages with lower pH's are better preserved
and more stable during feed out than high pH forages.
High pH forages are harvested either too wet or too
dry, which results in less than optimum fermentation
profiles. High pH forages are not stable and are prone
to spoilage, heat upon feed out, have a short bunk life,
poor palatability, and cause low dry matter intakes,
milk production and milk components. The measurement
of forage pH along with moisture can be used to evaluate
whether a forage is stable or prone to spoilage.
Lactic acid is the most effective acid
for reducing silage pH, thereby conserving high quality
forage. The higher the lactic acid the better the forage
quality. High quality forages are essential to support
high milk production, while minimizing acidosis and
health problems. Harvesting forages outside of the recommended
moisture concentration results in lower concentrations
of lactic acid, while the highest lactic acid concentrations
(Figures 3 and 4) occurred when forage were harvested
at the proper moisture concentrations. Ensiled forages
with the highest lactic acid concentrations tend to
be more nutrient dense, more palatable and sweet smelling,
which results in greater nutrient intakes.
Harvesting forages with higher than recommended
moisture contents (> 70%) can result in a deleterious
or abnormal fermentation resulting in high acetic and
butyric acid concentrations. High pH (>5.0) and butyric
acid concentrations usually occur together and would
indicate that a clostridial fermentation has occurred.
These forages may have a strong foul smell, are unpalatable
to dairy cattle, and cause low dry matter intakes. The
growth of Clostridia causes excessive protein breakdown,
which can result in an ammonia type smell. The ingestion
of clostridial forages may cause health problems, including
death of the animal. In addition, high butyric acid
forages are known to cause ketosis in transition dairy
cows.
Knowing the pH and lactic acid concentrations
of forages can provide additional information about
the quality of that forage for meeting the nutrient
requirements of dairy cattle. This information, in conjunction
with current nutrient measurements, will provide better
information for formulating dairy rations. The value
of these tests will be to identify those forages that
have undergone abnormal fermentation (i.e. high pH's,
acetic acid, and butyric acid with low or little lactic
acid) that can not be identified by standard nutrient
assays (i.e. poorly fermented, but acceptable nutrient
profile). Forages with high pH's and low lactic acid
concentrations may need to be fed in limited amounts
or eliminated from the ration.
Analyzing forages for their fermentation
profile has been gaining in popularity as a diagnostic
tool in evaluating animal performance related to forage
quality. Harvesting forages at the recommended moisture
concentrations in conjunction with the use of Silo King
will result in forages with the highest possible lactic
acid and lowest acetic (<2%) and butyric acid (<
.4%) concentrations that will maximize nutrient intake
by the dairy cow.
In summary, the forage fermentation profiles
can be used to evaluate the harvesting, storage, and
feeding quality of forages on your dairy operation.
Agri-King has been working on the development of methods
to rapidly analyze pH and lactic acid concentrations
in forages within 24 hours. Very shortly, pH will be
reported on the sample analysis page for fermented forages.
In the near future, lactic acid concentrations will
also be reported. Be watching for these values on your
sample test reports. If questions arise regarding the
interpretation of these values, please contact your
Agri-King Area Manager or the Nutrition Department.
