AMMONIA-NITROGEN IN FERMENTED FEEDS
SGS Agri-Food Laboratories has now added ammonia-N (NH3-N ppm) to fermented forage reports, such as
corn silage and haylage.
Ammonia-N in silage is produced by the breakdown of protein by either plant proteolytic enzymes, or
clostridial microorganisms (secondary fermentation). Although NH 3-N is not considered as protein (Nonprotein nitrogen-NPN), it provides N that can be used by rumen bacteria to synthesize microbial protein that
will provide the amino acids required by the cow for milk production.
For purposes of evaluation of fermentation or ration balancing, NH 3-N generated in silage is required as a
percentage of crude protein and in some cases as a percentage of soluble protein since NH 3-N will appear in
the soluble fraction of the protein. So, high levels of soluble protein in silages could be associated to high
NH3-N.
Increases in soluble protein can affect nitrogen utilization by microbes in the rumen if a good nutrient balance
is not considered (e.g. carbohydrate energy). Soluble protein and NH3-N are part of the A fraction or rapidly
degraded fraction of protein in the diet and high levels contributes to an excess of rumen-degradable protein
(RDP) with subsequent reduction of rumen-undegradable protein (RUP). Soluble protein is rapidly degraded
to ammonia in the rumen and is used by the rumen bacteria to growth. However, when the amount of
ammonia (available from rumen-degradable protein and urea recycling) exceeds the capability of the rumen
microbes to use it, ammonia is lost from the rumen into the blood stream and finally converted to urea that is
excreted in urine.
On the other hand, NH3-N in dry corn and high moisture corn is an indicator of fermentation associated to
storage time and starch digestibility of grain. Dry corn or freshly harvested corn (>15% moisture) does not
contain appreciable amount of NH3-N. So when corn does not contain NH3-N there is a high probability that
the corn is not fermented. Protein breakdown changes continuously with storage time. Increases in NH3-N
are observed up to six months of fermentation with a decline during subsequent months. High levels of NH 3N are also associated with breakdown of zein, the corn protein encapsulating starch granules. Zein in corn is
a major factor in ruminal starch digestion. It is believed that high levels of NH3-N in corn are partially
associated to breakdown in the zein protein making starch more rapidly degradable in the cow with
increased storage times.
Finally, silage NH3-N is the best indicator of fermentation quality. High NH3-N (>12 to 15% of CP) are usually
associated to clostridium fermentation that produce high levels of butyric acid, high pH and low silage quality.
Eelevated levels of butyric acid indicate silage deterioration with the presence of unpalatable nitrogenous
end products that lead to a reduction in DM intake and energy of the forage. Silages with less than 30% DM
have usually higher NH3-N concentrations because of the potential for clostridial fermentation. Silages
packed too loosely and filled too slowly also tend to have high NH3-N concentrations.
Importance of NH3-N:
Ammonia-N levels in fermented feeds are related to:
 Increases in soluble protein that can affect protein utilization by the cow as high levels of soluble protein
contribute to an excess of RDP and consequently reduction of RUP.
 Degree of fermentation in grain corn. When corn does not contain NH3-N there is a high probability that
the corn is not fermented.
 Breakdown in the zein protein of corn making starch more rapidly degradable.
 Good or poor fermentation in feeds. Ammonia-N levels higher than 12 to 15% of CP (depending on the
feed) may be associated to clostridium fermentation.
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