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Aflatoxin-contaminated kernels of grain are not evenly distributed in lots of grain, in mixed feeds, or in the field. This makes it very difficult to obtain a feed or grain sample which will accurately represent the level of aflatoxin in the original lot. Nearly 90 percent of the error associated with aflatoxin assays can be attributed to how the original sample was collected. Proper sampling is essential to obtain reasonably reliable test results. Failure to obtain a proper sample can result in unnecessary economic loss by causing loads of grain to be improperly rejected or by inadvertently feeding unsafe lots of grain to livestock.
Field sampling is difficult. Make one or more passes with the combine the entire length of the field . As the hopper is being emptied, pass a cup through the moving stream at 30 second intervals until a total volume of 10 pounds is collected. Mix the sample well and process quickly or dry it down to 13% moisture and store at cool temperatures in cotton, burlap, or paper bags for later processing.
The best method of sampling loads of grain is during loading or transfer. The recommended method is to pass a cup through the stream of moving grain at frequent intervals (ie. every minute) until the entire load is transferred and combine the cupfuls to form a composite sample of about 10 pounds. If the grain is not being transferred, probe sampling is acceptable. Use a double shelled, compartmented probe of sufficient length to reach the bottom of the container to obtain a representable sample.
Make probes in at least 5 locations (preferably more) to try to obtain a representative sample:
In both methods, mix the composite sample well before processing. If the sample is not going to be processed quickly, dry the sample to 13% moisture and place in cool temperatures to inhibit any further development of aflatoxin prior to testing. The samples must be finely ground so as to pass through a 15- to 20-mesh screen and be thoroughly blended to obtain a uniform sub-sample appropriate for analysis.
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