AFIA - Laboratory Methods Manual - Australian Fodder Industry ...

Step 2:
Convert the result to a true DM basis:-
Ad
(Af × 100)
=
TDM
where TDM = true DM content of the silage (g/kg)
Step 3:
Express the result as a % of total N (g/kg true DM) previously determined by Kjeldahl digestion
% Silage NH3-N of total N = Ad x 100
% N
Where % N = Total % nitrogen corrected for true DM content of the silage.
Comments:
• Silage is a fermented feed and the extent of breakdown of the protein or nitrogen (N)
fraction is a good indicator of silage fermentation quality. During the early stages of the
ensiling process, while anaerobic conditions are being established, and before there has
been a significant drop in pH, breakdown of the protein in forage (proteolysis) commences
due to the activity of plant enzymes. Further protein degradation can occur due to the
activity of undesirable bacteria, particularly if there is a delay in achieving anaerobic
conditions and/or there is a slow fall in pH. The ultimate breakdown product from this
process is ammonia-N. High levels of ammonia-N, expressed as a % of total N, are an
indicator of extensive protein breakdown and poor silage preservation. Ammonia-N is an
excellent indicator of silage fermentation quality, and for an interpretation of these results
refer to Kaiser and Piltz (2003).
• Silage is a perishable product and should be stored in a sealed bag (anaerobically) at low
temperature. If the sample is not to be analysed immediately it should be frozen.
• The use and interpretation of ammonia-N data as a measure of silage fermentation quality
is provided by Kaiser and Piltz (2003)
• Refer to the method for determining total N in silage. Where total N is determined on an
oven dried silage sample, failure to take account of the loss of volatile N will influence the
calculated result (% or g/kg total N). Also where total N is determined by the Dumas
method rather than the Kjeldahl method, some adjustment may be required for any
differences between the two methods in the total N result.
References:
AOAC Official Method 2001.11: Crude protein in animal feed, forage, grain and oilseed.
Kaiser, A.G. and Piltz, J.W. (2003). 12. Feed testing: assessing silage quality. In: “Successful
Silage”, eds A.G. Kaiser, J.W. Piltz, H.M. Burns and N.W. Griffiths (Dairy Research and
Development Corporation and NSW Agriculture: Australia), 24pp.
AFIA Laboratory Methods Manual – v7 September 2011 Page 30 of 103