Sampling Silage (Nutrition Update, Volume 8)

Editor's Note: The following is an excerpt from an excellent article by Dr. Dan Undersander, University of Wisconsin. Although Dr. Undersander refers to corn silage the points he makes are valid for all types of silages.

Forage analysis of corn silage is critical to balancing rations for maximum milk production on a least cost basis. Many are fooled by appearances, i.e. thinking that if the corn silage appears similar the quality has not changed.

In addition to corn silage differences caused by variations in hybrid maturity, soil type and other considerations, it is apparent that even a uniform initial material may change over time in moisture content and protein solubility. All of these considerations lead to the recommendation to sample corn silage from the silo frequently for analysis and to balance the ration accordingly. Corn silage should be sampled for analysis, as a minimum, by each field and hybrid.

One option available to producers is to sample chopped forage as it is going into the silo. The advantages of this system are: first, it may be easier to sample at harvest as the wagon/truck is being unloaded or from the bunker as it is being filled; second, analysis results will be available long before the silage is to be fed to allow inventorying and allocation of feed to best use, more accurate ration balancing and forward planning in purchase of supplements.

Some fractions (dry matter and protein solubility) show significant change during the ensiling and fermentation process but crude protein and fiber fractions (ADF and NDF) show little change where the forage was ensiled properly and normal fermentation occurs. Analysis will change when forage is ensiled at too high a moisture content and seepage occurs, when forage is ensiled too dry and heats excessively and if fermentation is faulty.

When prior to ensiling, one should keep in mind that the distribution of leaves and stems will not be uniform through the chopper wagon or truck because leaves are lighter than stem parts and often accumulate towards the back and sides of the wagon or truck while the center will have a higher concentration of stems. These fractions are mixed as the wagon is unloaded into the blower or as the load is spread in a bunker silo. Therefore to get a good sample from a wagon unloading into a blower, use a shovel to take three samples from the middle of the load as a wagon is unloading. Combine samples from several wagons from the same field and corn hybrid. In a bunker silo, samples can be taken from the middle of the wedge periodically during the harvesting of a field/hybrid. Send fresh samples immediately to the laboratory for analysis. Do not freeze fresh forage as this may increase fiber 3 to 6%.

Silos with seepage or excessive heating should be resampled upon feeding. All silage should be rechecked for dry matter on feed out. It is generally recommended that high moisture feeds be analyzed weekly for moisture content.

Source: Undersander, Dan. 1997. Proceedings. Silage: Field to Feedbunk. North American Conference, Pennsylvania,February 1997. 

Nutrition Update
Volume 8 No.2, August 1997