GRASS SILAGE
SAMPLING AND INTERPRETATION OF ANALYSIS
Silage Sampling


Sampling should be conducted at least six weeks after harvesting to ensure fermentation has completed. Sample early in the week and post
for next day delivery.
Provide as much of the additional Information required by the input sheet, as possible (e.g. crop type, grass silage cut; 1st, 2nd or 3rd etc.), to
assist the analysis and interpretation of a seasonal picture.
On Farm Sampling
 Visualise a ‘W’ pattern on the face of the silage clamp. Take at least 9 samples from 15 – 20cm behind the face at different horizontal and
vertical positions on this ‘W’. Only sample areas where mould is present if these areas of the clamp will be fed.
 Preferably samples should be prepared by ‘Quartering’; tip the sample onto a clean board and thoroughly mix it. Using a piece of clean
board, divide the sample at right angles into four piles to achieve a final sample size of 0.5kg. Place the entire 0.5 kg sample into a clean
plastic bag and ensure as much of the air is removed, as possible.
For further information see the Forage Analytical Assurance Group website - http://www.faagroup.co.uk/
Interpretation of Grass Silage Analysis
Term
Implication for Rationing
Typical
range
Dry Matter
(%)
The quantity of material left in a feed after all the water has been removed by drying. The value is corrected to allow for
losses of volatile but nutritionally valuable nutrients during drying, e.g. volatile fatty acids.
25 - 45
Protein (%)
D Value (%)
ME (MJ/Kg)
Low dry matter silages tend to be extensively fermented and will be high in acids and low in rumen structure, reducing
intakes. High dry matter silages are more susceptible to spoilage (bacterial and fungal).
This is calculated from the total nitrogen content of the silage multiplied by 6.25 as the average nitrogen content of
protein is presumed to be 16%. This value provides no information on the quality of the protein in the silage.
If high, additional protein tends to be rapidly degradable and may be poorly utilised, especially if there is inadequate
rumen available energy in the diet. High milk and blood urea levels have been associated with feeding this type of silage;
the latter can have a direct and indirect impact on fertility.
A measure of the digestible organic matter content in the dry matter. This value is inversely related to the crop’s stage of
maturity at cutting.
Metabolisable Energy – a measure of the energy content of the feed available to the cow after losses in, faeces, urine
and methane. It is predicted from the ‘D value’.
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11 - 15
67 – 73
10.5 – 11.5
GRASS SILAGE
SAMPLING AND INTERPRETATION OF ANALYSIS
pH
NH3-N of
Total N (%)
Sugars (%)
Ash (%)
NDF (%)
ADF (%)
Oil (%)
Vitamin
E(mg/kg)
MPB (g/kg)
MPN (g/kg)
‘sN’ ‘aN’ ‘bN’
‘cN’
MPE (g/kg)
A measure of the acidity or alkalinity of the silage; pH < 7 = Acidic, pH 7 = Neutral, pH > 7 = Alkaline. Where the pH of grass
is above this range, typically as a result of poor or secondary fermentation, undesirable VFA’s may have been formed and
production may be reduced. When feeding out, products such as ‘Regulator Feed Out’ can be incorporated to reduce
further heating and mycotoxin binders e.g. Ultrasorb, can be used to minimise the mycotoxin challenge. Conversely
feeding more acidic silages may impair rumen performance, resulting in acidosis, lower intakes and production. Feeding
rumen buffer products such as Acid Buf® can help to alleviate this problem.
High values are indicative of butyric fermentation and may be associated with high blood and milk urea levels; high
blood urea has been both directly and indirectly linked to infertility. Care should be taken in interpreting this term as it is a
percent of total N and not a percent of the dry matter.
The sugar content of the silage remaining after fermentation. This value will be affected by the extent of fermentation i.e.
extensive or restricted and tends to be directly proportional to the dry matter content of the silage.
A measure of the total mineral content. Values above 9% may indicate soil contamination during ensiling. Soil is rich in iron
and will ‘lock-up’ the copper content of the silage. The animal’s phosphorus uptake may be reduced. This problem can
be overcome by feeding organically bound trace elements such as ‘Availamins®’.
The Neutral Detergent Fibre value indicates the total fibre content of the plant and includes the hemi-cellulose, cellulose
and lignin residues. High NDF levels are associated with mature crops at cutting.
The Acid Detergent Fibre value is similar to the NDF but only measures the amount of cellulose and lignin in the silage.
The ratio of ADF to NDF is indicative of the proportion of digestible fibre in the forage.
Oil is an important energy component of the silage however too higher oil content can interfere with the activity of the
rumen microbes.
Vitamin E is important in dairy cow rationing due to its role as an anti-oxidant, in immunity (particularly mastitis) and fertility
(including cleansings and metritis). Ruminants are unable to produce Vitamin E and therefore require a regular dietary
source.
Metabolisable Protein from Bypass Protein (also called DUP). Protein which is protected from degradation in the rumen.
This fraction is important when rationing high yielding dairy cows as the rumens supply of metabolisable protein for milk
production is limited. The MPB content of the ration should be increased to reflect greater milk yields using products such
as SoyPass®.
Metabolisable Protein supply from the silage where rumen nitrogen (protein) is limiting. It is typically greater than MPE as
rumen energy is usually the limiting factor in a ration. High levels of MPN in the ration can, indirectly, negatively influence
fertility.
Rumen degradable fractions; these values measure the instantly soluble (sN), rapidly degradable (aN) and potentially
degradable (bN) protein fractions of the silage. The rate of fermentation of the potentially degradable fraction (bN) is
described by ‘cN’.
The ‘Metabolisable Protein supply where rumen energy is limiting’. The energy for the rumen microbes is provided by the
sugar, starch and fibre components of the silage and tends to be the limiting factor in rationing.
2/3
3.8 – 4.2
3-6
2-4
5 – 10
45 - 55
30 – 40
3–5
15 - 50
35 - 50
85 - 110
N/A
75 - 90
GRASS SILAGE
SAMPLING AND INTERPRETATION OF ANALYSIS
‘sDM’ ‘aDM’
‘bDM’ ‘cDM’
VFA’s (g/kg)
Lactic Acid
(g/kg)
Intake (g/kg
ML)
Rumen
Stability
Value
FiM PAL
(meq/kg)
Rumen degradable fractions; these values measure the instantly soluble (sDM), rapidly fermentable (aDM) and potentially
fermentable (bDM) dry matter of the silage. The rate of fermentation of the potentially fermentable fraction (bDM) is
described by ‘cDM’.
The percentage of Volatile Fatty Acids (predominantly, acetic, propionic and butyric) produced during silage
fermentation. Lower values are desirable as they indicate a stable silage.
The main acid produced during the natural fermentation of sugars in silage. Poor preservation results in higher levels of
undesirable acetic and butyric acids from secondary fermentation. Lower levels are associated with restricted
fermentation e.g. wilted and chemically restricted.
A relative indication of how much silage a standardised cow will eat by choice. It is influenced by a mix of the dry matter,
crude protein, digestibility, fibre fractions, VFAs and ammonia N concentration of the silage; typically, higher intakes are
indicative of higher quality silages. Dry matter, digestibility and protein are positively related to intake. The Feed into Milk
ration program converts this value into specific intakes for the cow being rationed.
An indication of how stable the rumen will be when fed the silage, it is calculated from the NDF and Potential Acid Load
(PAL). Silage with low RVS’s values may reduce the pH of the rumen, leading to acidosis and reduced intakes. The Feed
into Milk ration program considers this in conjunction with other ration components and cow details to predict the overall
effect on rumen health.
The Potential Acid Load represents the silage fermentation acids, those produced by the rumen micro-organisms during
digestion and any other feed components e.g. amino acids. Rations containing a high PAL content will typically have a
low RSV.
3/3
N/A
20 - 40
50 - 100
90 - 120
200 - 400
550 - 1000