The Art of Sample Collection:
Sampling Concentrate Feeds
Dr. Duarte E. Diaz
This is the last part of a three part series on sample collection. Today we will discuss techniques for sampling concentrate feeds.
Theoretically, concentrate samples should be easier to sample compared to silage because with the proper equipment and the right approach you should have access to all portions of the feed (silage is more difficult since we can generally only sample from the face).
When sampling from bins or trucks a sampling probe is the most effective way to collect samples. Probes are traditionally made of aluminum and of different sizes and lengths. The size of the probe opening should large enough so that the largest particle size in the particular feed cannot be excluded. The Grain Inspection, Packers and Stockyards Administration (GIPSA) recommends the following probes:
GIPSA approved probe sizes for sampling stationary lots of grain.
5 or 6
6, 8, or 10
10 or 12
Other probes may be used such as the core probe and the gravity fill probe. In general a minimum of 5-10 samples should be taken using the probe and making sure that the probe is at a ten degree angle. The samples should be mixed thoroughly and a sub-sample collecting using the quarter system. If a probe is not available a hand scoop of a minimum 1 cup capacity should be used to collect from 6 to 12 samples from random locations throughout the bin or truck. These samples should also be mixed thoroughly and sub-sampled before sending out for analysis. At least 1 pound, or a quart of material, should be sent to the laboratory. Hand grab samples should never be collected as they exclude smaller size particles that may seep through your fingers. For pelleted feeds, scoops of pellets should be selected from at least 15 locations and a sub-sample containing a minimum of 1 pound of pellet is selected for analysis.
Finished feed should be sampled as they are being put out in the feeders. Although you could potentially collect a finished feed sample from the feed bunk, ideally you should collect your samples during discharge of the feed into the feeders. Several samples at different times should be collected to ensure a more representative sample.
Commodity feeds should be analyzed as a composite of at least 10-15 areas of a given lot of feed. When mixing the composite, avoid segregation by particle size or the true sample value may be distorted. These results represent only
the bulk averages and will not give you information on the uniformity of nutrient content within the mix. If you're experiencing inconsistent herd performance using these feeds, the uniformity of the mix may be questionable and a different technique should be employed. Taking several samples of the commodity and having each analyzed will allow the producer or feed nutritionist to do a better job of adjusting the ration to accommodate the feed differences.
Not all feed need to be analyzed with the same frequency. Feeds with low variability (i.e. corn and soybean) don�t need to be analyzed as frequently and in some cases not at all. For these low variability feeds, you can get good results from using book values but you should definitely analyze them if you suspect that your particular feed is different (i.e. poor looking grains, extreme weather conditions, etc.).
For feeds with moderate (i.e. wheat, barley and oats) or high variability (i.e. distillers dried grains and bakery waste by-products) in nutrient composition, routine feed sampling and analysis is essential. You may be saying to yourself that by the time you get a sample report back from the laboratory, the feed has been fed. However, the importance of this data is to obtain the mean composition which will help in proper feed formulation. The values obtained from a single submitted feed sample are not as important as the series of analyses. The series of analyses provide you the most information in formulating the ration. The frequency of sampling depends on the expected variation and how much error you are willing to accept. In general, analysis should definitely be sought out when any changes are implemented in the form of a new ingredient or a change in the source or location of a specific ingredient. As a general guideline, ten or so analyses a year of a given population is reasonable. Always adjust up or down depending on the variability of the feed.
Unexpected or varying results should trigger the following question �Why did the composition changed?� Possible answers to that question include: �I changed suppliers�, �the distillery changed production methods�, or probably and most commonly, �I don�t have an idea�. If you cannot think of a good reason the composition changed or varied so much, the value may simply be a random event. The difference could be caused by load-to-load random variation, within load (i.e., sampling) variation, or both. In this case, the new should not be used for formulation.
The take home message from these three articles is that improperly sampled feeds will invalidate any analysis. So to make the most of your time (sampling) and of your money (analysis and ration balancing) make sure that you spend the appropriate time and care collecting samples that are to be analyzed. With a little planning and the right tools proper sampling techniques can be implemented in our everyday farming routine without much hardship.