Physical and chemical tests for silage quality 2

 The quality of silage is highly dependent on the quality
of the forage harvested and the type of fermentation
that has occurred.
These factors will influence the:-
 Palatability to livestock
 Livestock productivity
 Dry matter losses
 The risk of toxins forming in the silage
composed by Touqeer Yazdan 2

 For any silage or feed tests use a clean airtight bag or
Feed Test Bag
 Representative samples must be obtained from the silo
and the samples must be handled properly prior to
analysis
 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
 Avoid taking samples that have been exposed to
oxygen as they may have deteriorated and not be
representative of what is being fed
 Silage samples may be refrigerated or frozen before
shipping to aid in preservation during transit
 Include ice packs and place in a shipping cooler if
practical

 Commonly following two physical tests are
involved/used to check the quality of a silage sample.
1. By checking the appearance of a silage sample
And by
2. Smelling the silage sample

Appearance
 Good silage is light brown or greenish in color
 Otherwise it is spoiled or not fermented well

 There are several common odors that one can detect when
smelling silages. These odors can tell you what happened in
the silo and are often related to silage quality.
1. A very “sweet” smelling silage is not always an indicator
of the best fermentation
2. In contrast, a “foul” smelling silage is a pretty good
indicator that something has gone wrong
3. In some corn silages, a “nail polish” like smell may be
present. Compounds like phenyl-acetic acid may be
responsible for this smell. (To date, we are unsure of the
significance of this smell in silage)

 Well, the best type of silage fermentation – called
homolactic acid fermentation – should have little or
no distinct smell because the dominant acid produced
via this process, lactic acid, has almost no smell.

 pH
 Dry Matter (%)
 Crude Protein (%DM)
 Acid Detergent Fiber (%DM)
 Neutral Detergent Fiber (%DM)
 Digestibility [DOMD] (%DM)
 Metabolisable Energy [ME] (MJ ME/kg DM)
 Soluble Sugars (%DM)
 Starch (%DM)
 NH4-N:Total N (%)
 Lactic Acid (%DM)

 Quality of silage can be assessed by making visual
observations and with the help of several simple
analytical tools.
Silage evaluation equipment include a:
1. pH meter or litmus paper
2. temperature probe
3. Microwave moisture tester
4. scale
5. silage density probe
6. Penn State forage particle separator screens

pH is a key criterion to evaluate silage fermentation.
Generally the lower the pH, the better preserved and more
stable is the silage
 The pH of silage measures the degree of acidity. A pH of 7
is neutral and numbers less than 7 indicates acidic
conditions
 A silage sample can be prepared by vigorously shaking a
small sample of silage with 100 ml of water (about 4 fluid
ounces) for a minute or two
 Then insert a pH litmus paper strip or meter probe into the
silage for 1-2 seconds
 A pH-sensitive paper can be dipped into the liquid and will
change color-based on the degree of acidity

 A hand-held battery operated pH probe can give a
more accurate measure of acidity
 The meter will deliver an instant pH reading on the
LCD display, while the color change of the litmus
paper test strip is compared to a color key that
corresponds with appropriate pH (the color key is
found on the side of the pH litmus paper container)
 Well preserved corn silage will have a pH in the range
of 3.7 to 4.2

 To calculate dry matter, you can use various methods,
including: a microwave oven, or a Koster Moisture
tester
 In each instance, you need to measure the weights of
the sample before and after drying (to determine the
amount of water driven off by drying)
 Usually three readings are taken to check dry matter
 If all the readings give same results it means your
results are correct

Some example calculations:
Before drying-- 85 ounces
After drying -- 25 ounces 25/85 = 29.4% dry matter
 (As is yield) x % dry matter = dry matter yield
If you harvested 23 tons of corn silage at 29.4% dry
matter
 23 x 29.4% = 6.76 tons of dry matter per acre

 Final Dry Weight (g)/Initial Wet Weight (g) X 100 =
………% Dry Matter
 Example 1. 50 g X 100 = 33.3 % DM
 150 g
 Example 2. 48 g X 100 = 42.8 % DM
 112 g
 Note: Have you allowed for the weight of the plate?

 Lactic acid is the strongest and most abundant acid
produced during an ideal fermentation
 Moderate levels of lactic acid are an indication of good
fermentation. The lactic acid content of good corn and
alfalfa silage ranges from 4 to 6% and from 3 to 8%,
respectively on a dry matter (DM) basis
 Of the volatile fatty acids (VFA), acetic acid is found in
the greatest concentration and butyric and propionic
acids are uncommon end products of normal silage
fermentation

 The acetic acid content of corn and alfalfa silages is
usually between 1 to 3% and butyric acid content
should be undetectable in good silages
 The ratio of lactic acid to acetic acid is a good indicator
of the efficiency of the silage fermentation
 Poor ratios of lactic acid to acetic acid indicate that
you should consider using a microbial inoculant
containing homolactic acid bacteria when ensiling
 Ideally, the ratio of lactic acid to acetic acid should not
be less than 3:1 and higher is better

 Determination of individual acid content is usually
accomplished by some type of chromatography
 However, some labs use enzymatic methods to detect
lactic acid
 In this case, the L-form of lactate is determined and
then multiplied by 2 to obtain an estimate of total
lactate (since the L- and D- forms are usually present
in a 1:1 ratio).

 Ammonia concentration is usually expressed as a
percentage of the crude protein (CP) or nitrogen
content
 In corn silage, ammonia is normally between 5 to 7 %
of the CP but it is usually higher (10 to 15%) in grass
and alfalfa silage
 High concentrations of ammonia are an indicator of
extensive protein degradation
 Ideally, ammonia should be <7% of the protein content
but this is difficult to achieve in high protein forages
(e.g. alfalfa)

 Ammonia can be determined by colorimetric or
distillation procedures or with an ammonia-specific
ion probe

 The phenol - hypochlorite method, produced as a
clinical chemistry kit, can be used for the
determination of urea in water extracts of compound
feed and of chopped, fresh silage
 This method is simple, rapid, inexpensive and may be
automated for the determination of urea used as
supplementary nitrogen in compound feed and silage.

 In addition to determining chemical products, some
analytical labs will enumerate(count) the numbers of
yeasts and molds in silages
 Yeast and molds are determined by growing them on a
selective medium
 The number of colonies formed on a petri plate with
this media are counted and expressed as colony
forming units (cfu) per gram of wet silage
 High numbers of yeast and molds are usually an
indication of poor packing of a feed or a too slow feed
out rate that exposes silage to oxygen

 Silages with more than 100,000 (or 1 ´ 105 cfu per gram
of silage are usually prone to rapid heating and poor
bunk life(because many yeasts degrade lactic acid and
are the cause for spoiling when silages are exposed to
air)

Item
Alfalfa Silage, 30 -
35% DM
Alfalfa Silage, 45 -
55% DM
Grass Silage,25 -
35% DM
Corn Silage, 35 -
40% DM
HM Corn, 75%
DM
pH 4.3 - 4.5 4.7 - 5.0 4.3 - 4.7 3.7 - 4.2 4.0 - 4.5
Lactic acid, % 7 - 8 2 - 4 6 - 10 4 - 7 0.5 - 2.0
Acetic acid, % 2 - 3 0.5 - 2.0 1 - 3 1 - 3 < 0.5
Propionic acid, % < 0.5 < 0.1 < 0.1 < 0.1 < 0.1
Butyric acid, % < 0.5 0 0.5 - 1.0 0 0
Ethanol, % 0.5 - 1.0 0.5 0.5 - 1.0 1 - 3 0.2 - 2.0
Ammonia-N, % of
CP
10 - 15 < 12 8 - 12 5 - 7 < 10

Physical and chemical tests for silage quality 2

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