Sampling Corn Silage for Analysis

Most forage testing laboratories do reasonably well at analyzing the "received" sample. The major problem in balancing rations is whether or not the analyzed samples represents what is being fed. Most laboratories will do dry matter and other analysis on approximately a 100 to 150 g sample. Larger samples are subsampled and only the Subsample analyzed.


A. Upright silos
                - Run out at least a feed cart full of material. Take 10 - 15 subsamples, composite and send this in.

B. Bunkers -
                -Take 10 - 15 samples in a grid approach representing the area fed out daily. Composite and send the composite in. It
                   is best to use a corer to sample at least 8 to 10 inches into the face.
                - Alternately, take subsamples from several places/loads in the loader bucket


                -Comments of feed sales reps:

                    1) Sampling face of bunker is not good:

                            a) dry matter not right

                            b) face of silage could slide down and bury person sampling

                    2). Hand sample of silage may bias particle score because fingers act as screen. Must use a scoop to get sample

                    3). Frequently there is a large layer of dry or spoiled silage where the harvest had to stop for a day or two because of   weather. 
                          This could affect sample.

  C. Sampling from TMR mixer. (Best) - An alternate method is to load silage from upright or bunker silo into a TMR mixer, mix and sample. Send this sample to the lab.


D. Sample silage as silo is being filled. - take several samples from wagon/truck, as it is unloading and composite. Send this sample to the lab. (see next page)



The real challenge is that sampling takes time and many feed rep's don't have time to do this. If visiting 4 - 10 farms per day as a feed person, how much time can be spent per farm? Perhaps, the dairy producer must do the sampling.

All of the above (except D) sample what is being fed today. This may be acceptable to balance a ration for next week if the vertical silo was filled rapidly (in 1 or 2 days) or the bunker silo was filled in wedges over a short time (2 to 4 days). Sampling today’s feedout to predict next week’s feed will not be acceptable otherwise due to variation in the silo (see graphs below).
                                       Silo Depth refers to distance in feet from height above ground in a vertical silo
Sampling at harvest gives you advance knowledge of the quality of silage stored in the silo. One can inventory and plan for purchasing supplemental feedstuffs based on forage quality needs.


While some fractions can show significant change during the fermentation following ensiling, crude protein and fiber fractions (ADF and NDF) show little change where forage was ensiled properly and normal fermentation occurred (see table below). Analysis will change when:

    1. Forage is ensiled a too high a moisture content and seepage occurs (crude protein and nonfibrous loss resulting in higher fiber)
    2. Forage is ensiled too dry and heats excessively (acid detergent fiber and acid detergent fiber insoluble nitrogen increase)
    3. Fermentation is faulty so that excessive mold growth occurs.
  Table 1. Forage quality analysis before and after ensiling from repeated sampling during 1988 and 1989, University of Wisconsin Ashland Research Station.


Before/after          Dry

Ensiling                 matter     CP    ADF    NDF

                                    Alfalfa Haylage

                    Before                   44.1      19.9    32.3    40.5

                    After                      42.4      20.7    34.8    40.4


                                Corn Silage

                    Before                   34.4      9.7     29.2     49.5

                    After                       34.1   11.1     29.0     48.8