More Questions and Answers on Moldy Grain, Mycotoxins
Q. Why is there such a within load variation for vomitoxin ppm? For example, a load can test zero ppm at one elevator and 10 ppm at another elevator.
Response: Variability stems from the fact that there is variation in the number of ears infected within a field and, on any given ear, there is variation in the number of kernels infected, and even more, kernels with similar appearance in terms of moldiness on the surface, may have different levels of internal fungal colonization and consequently variation in mycotoxin contamination. In addition, healthy-looking kernels may also be contaminated with vomitoxin. Variability is a major issue!! Because of this variability, sampling needs to be done correctly in order to adequately determine the level of contamination. There are always “hot spots” within the grain lot and if you sample only once or a few time and end up doing so in those “hot spots” then you’ll overestimate how contaminated the grain lot really is. Conversely, if you totally miss the hot spots then you’ll underestimate contamination. That’s the reason why we always recommend that multiple samples be taken from multiple locations within the lot, then bulk, mix and grind the grain before analysis.
We (OSU) have not used all of the testing equipments that are out there, but most of the highly recommend ones are fairly reliable and consistent. The kits that give you quantitative estimates (1,2,3,15,38 ppm) are generally better that the semi quantitative (more than 5 ppm) or qualitative (yes/no response) kits… but it all depends on what you are using the kit for. In general, the ELISA kits (most of the kits that are out there are ELISA-based) are calibrated against the more sophisticated quantitative lab equipment, and if used correctly (incorrect use is another potential source of variation) should provide consistent results across elevators. However, test results from one elevator to another are also subject to variation in how the samples were drawn from one elevator to another. Unless the sampling is done correctly and in the same or a similar manner among elevators, it will be impossible to tell whether the differences (0 at one elevator and 10 at another) are due to differences among the testing equipments or to poor and inconsistent sampling protocols among elevators. In fact, the best way (but probably not the most practical) to compare elevators it to send subsamples from the same bulk sample for testing at the different elevators.
Q. For on-farm separation of mycotoxin infested corn from clean corn, would a gravity table work satisfactorily?
Response: Very moldy kernels are usually lighter than healthy, plump kernels, however, like I in the paragraph above, plump-looking kernels may also be contaminated with vomitoxin. Any method that can be used to remove moldy kernels will help to reduce the overall level of contamination of the lot… moldy kernels are always more contaminated that the most contaminated of the healthy-looking kernels.
Q. Is there a possibility of the probe itself being a cause for some of the variability in readings? Can the mycotoxin be transferred to clean corn from a probe?
Response: Although the probe can more the mycotoxin-producing fungus around, the probe is generally not a means by with the mycotoxin itself moves from contaminated to clean corn. If the corn is indeed clean (with little or no fungus) and stored correctly, then the small amount of fungal mycelium or spore carried on the probe should not be sufficient to cause major contamination of the healthy lot. However, on the subject of cross contamination, it is never a bad practice to clean the probe before moving between lots or loads.
Part I of mycotoxin issues can be read at http://wp.me/peijs-p9
Full podcast here: