Storm-Damaged Corn: Tips for Testing and Feeding
Any time a growing grain-producing plant is damaged, there is a potential for changes in the plant or grain on the plant contaminated with fungus/molds to grow. The most common change in stressed plants is the accumulation of nitrates.
Aspergillus or Fusarium will be the most likely fungi to be contaminating harvested grain from storm-damaged corn in south central Nebraska.
It is really important to know that most molds are not toxic. Therefore just because mold growth is observed doesn't mean the feedstuff will harm livestock. Even though a mold may not be toxic it can still cause feed refusal. Not all livestock species are equally sensitive to mold contamination and not all production groups are equally sensitive. For instance pregnant and young animals are more sensitive than mature non-pregnant animals.
Nitrate accumulation in stressed plants can be harmless or cause serious harm depending on:
- the level of nitrate in the feed harvested from stressed plants,
- the life stage of the animal, and
- the species of animal.
Nitrates accumulate in the forage portion of the plant, so nitrates are not a concern in grain harvested from stressed plants. Additionally, it is important to know nitrate levels will always be highest in the bottom part of the plant and lowest in the top foliage. Nitrate testing is simple and reasonably quick. Your local UNL Extension Educator can help you locate the nearest facility that does forage nitrate testing.
Feed containing a nitrate level less than 1000 parts per million (ppm) seldom is associated with an animal health concern. Feed containing a nitrate level greater than 1000 ppm may be a concern in younger animals and levels over 2000 ppm should not be fed to pregnant cattle. Feeder cattle are reasonably resistant to nitrates but feeds containing more than 4000 ppm should not be fed to any animals.
Molds in corn grain of concern could be either Aspergillus or Fusarium. Your UNL Extension Educator can be a great help in identifying mold growing on ears of your storm-damaged corn before the grain is harvested. Both of these fungi are potentially dangerous when found in livestock feed. Toxins produced by molds are extremely stable, therefore if a significant level is found, the level will not decrease over time. Silage produced from damaged plants and grain harvested from mold-infested plants is potentially a problem.
Good silage management is critical to reducing the risk of continued mold growth after ensiling. Proper packing to remove oxygen and improve fermentation is critical to ensuring that the pH stays below 4.5.
You can't look at harvested grains from storm-damaged fields and visually identify mycotoxins. Corn grain from storm-damaged fields can - and mostly likely should - be tested for mycotoxins before feeding to livestock. Your local UNL Extension Educator, nutritionist or veterinarian can help with mycotoxin testing.
Recommendations on Sampling
Proper sampling is crucial to getting reliable results back from the laboratory. A grab sample is not adequate. The sample submitted to the lab should be representative of the entire load, bin, pit or pile of feedstuff being evaluated.
The steps are simple
- If sampling a field before harvest, sample at least two dozen ears that appear to have mold growth and submit all the ears to the laboratory for mycotoxin evaluation.
- If sampling after harvest, take multiple samples uniformly from throughout the silage or grain in question.
- Take the sample from what would be used in a single load of feed. That means, if five loads of feed could be made from a 50,000 lb semi-load of corn, collect at least five samples from the semi-load of corn.
- The sample should be based on sample volume not weight. For instance, collect coffee can size samples.
- Mix all the all samples together that were collected from the feed in question. For example, if 10 coffee can size samples were collected from across the face of a silage pit, pour all 10 samples onto a plastic sheet and thoroughly mix them together. Then, collect a single sample from within the 10 mixed samples.
- Submit the single sample to the laboratory
The laboratory results usually will provide some recommendations for how the feedstuff can be used. There is an old saying, Dilution is the solution … meaning in this consideration, that many feedstuffs that contain higher levels of mycotoxin than would be acceptable, might be usable if a sufficient amount of non-mycotoxin contaminated feedstuff is used to dilute the mycotoxin. Your UNL Extension Educator, nutritionist, or veterinarian can help evaluate the possible uses of a damaged feedstuff containing unacceptable levels of a mycotoxin.
Dee Griffin, DVM
UNL Great Plains Veterinary Educational Center, Clay Center